Colony Initiation Research Articles

Variation in Life-History Pattern in Relation to Worker Mortality in the Bumble-Bee, Bombus lucorum

We experimentally varied worker mortality in laboratory colonies of Bombus lucorum to test for the effect of mortality occurring either early or late during the colony cycle on further development and eventual reproductive performance. Ten per cent of the workers were removed each day during 2 weeks immediately after eclosion of the second brood in 'early-stressed' colonies. The same percentage was removed for 2 weeks but 15 days after eclosion of the second brood in 'late-stressed' colonies. Such variation with respect to colony cycle could result from parasitization of worker bees by endoparasitic larvae of conopid flies (Diptera: Conopidae) at different times of the season. Neither earlynor late-stressed colonies compensated by producing more and/or smaller workers as compared to the controls in which no workers were removed. But stressed colonies invested on average less into male production in terms of biomass and numbers; no differences existed for gynes. Total biomass put into sexuals differed with group and sex ratios were highly skewed towards males. Body sizes of gynes, on the other hand, were somewhat smaller in stressed colonies than those produced by the control colonies. Start of reproduction, i.e. emergence of first sexuals in days after colony initiation and number of workers present at maturity, did not vary among treatments. We conclude that at least for the present experiment, environmental perturbation increasing worker mortality rate affects male numbers while in gynes body sizes decrease. Early stress had more effect on males, late stress more on production of gynes.

The relationship between growth form and internal morphology in favositid corals

Growth form in Paleozoic colonial corals is commonly used as an indicator of paleoenvironmental conditions. However, this character was also influenced by genetic factors, and it must be recognized that aspects of internal morphology were significant in the development of external form. In favositids a primary control on growth form was exerted by rates of corallite divergence, offsetting, and vertical growth, since the shape of the corallum base and growth surface resulted largely from these factors. This relationship worked in both directions; modifications of external shape that were apparently related to environmental conditions are reflected by measurable changes in internal morphology. In any favositid the most efficient packing of corallites is hexagonal, but this arrangement was thrown out of equilibrium by corallite offsetting. Rate of offsetting was largely controlled by internal packing stress and thus by the degree of corallite divergence. Periodic offsetting is reflected by a bimodal corallite size distribution (dimetrism). The distribution of corallite shapes and sizes in different parts of a corallum is therefore a key indicator of mode of growth; growth form can be seen to have had an influence on characters that are commonly used as species discriminators.This study is based on analysis of serial sections of Paleofavosites subelongus (Savage) from the uppermost Ordovician to lowermost Silurian of the east-central United States. This species is highly variable in internal characters and the size range and type of corallite packing can differ substantially between coralla. The early part of each colony's astogeny played a major role in the development of growth form; specimens at either end of the variation continuum show contrasting modes of growth which generated different growth forms. In one mode, colonies produced broad bases through early axial offsetting and developed patterns of growth in which corallites expanded rapidly to mature sizes. Subsequent rates of offsetting were sufficiently high that dimetrism is common; such specimens most commonly have domical growth forms. In a second mode, colonies with lower rates of early axial offsetting have conical bases, a lower degree of dimetrism, and commonly bulbous forms.Patterns of subsequent growth of all coralla demonstrate the connection between internal and external characters. Periods of increased axial offsetting and higher rates of corallite expansion occurred in conjunction with phases of lateral colony expansion. Elsewhere in the colony, offsetting was also periodic but occurred predominantly at the edges of the axis and in colony margins; this pattern allowed the axial polyps to continue upward growth while shorter-lived polyps were generated to maintain lateral parts of the growth surface. Bursts of offsetting commonly occurred in bands with close-spaced tabulae and thickened corallite walls, and were sometimes associated with intervals of increased corallite mortality. Paleofavosites subelongus was apparently unable to produce offsets at the outermost colony margins and was thus confined to upwardly expanding growth forms with outcurved corallites. Serial sectioning of other species of Paleofavosites in which tabular forms predominate indicates that coralla with such shapes were able to generate abundant offsets along colony margins and could maintain axial regions with predominantly hexagonal corallites and low rates of offsetting.Although internal characters apparent early in astogeny set the basic mode of growth of each Paleofavosites subelongus colony, the subsequent growth form was influenced by numerous other factors, including reorientation during life, partial mortality of the growth surface, and probable changes in environmental conditions. In most populations one of the two modes of basal growth predominates, but populations with overlapping characters also occur. The growth pattern set down near the base of each corallum may be related to the environmental regime prevailing at and following the time of colony initiation, but may also reflect genetic differences within and between populations.

The transition from germ tubes to vegetative growth in uredospores of Melampsora lini

The transition from uredospore germ tubes to vegetative hyphae marks the initiation of mycelial colonies of Melampsora lini growing in axenic culture. It is promoted by heat shock (31 °C for 2 h) and is arbitrarily defined as having occurred when mitotic divisions of the two original uredospore nuclei have produced more than four nuclei. The percentage of germinating spores in which it occurs (percentage initiation) does not increase beyond 48 h after seeding and is higher (about 9 vs. 5%) at a low (18 spores/mm2) than at a higher (90 spores/mm2) inoculum density. The number of nuclei in a mycelial colony arising from a single uredospore increases exponentially with a mean doubling time of 2.40 days. Neither the percentage initiation nor the rate of increase in number of nuclei (= mycelial growth) are affected by the proximity of neighbouring spores at spore densities of the order of 18 spores/mm2. Approximately 10% of the initiated colonies exhibit a growth rate that renders them visible to the naked eye after 5 weeks. Key words: rust fungus, axenic culture, vegetative growth, single spore colonies.

Dynamics of biparental care in the dampwood termite, Zootermopsis nevadensis (Hagen): response to nitrogen availability

Studies were conducted on the dampwood termite, Zootermopsis nevadensis, to examine the behavioral roles of the reproductive pair during the nest-founding period and to determine the effect of nitrogen availability on their reproduction and division of labor. Nitrogen has been hypothesized to be an important limiting nutrient for founding pairs. One nitrogenous reserve, uric acid-nitrogen, was examined in reproductives and in nutrient-receiving and nutrient-gathering colony members; it was found in highest amounts in the reproductives (i.e., alates, de-alates, and primary reproductives). Young pairs may use these nitrogenous reserves to increase their chances for reproduction. In support of this hypothesis, founding pairs that were fed a diet supplemented with uric acid-nitrogen had a significantly greater probability of producing at least one offspring than did pairs fed an unsupplemented diet. Females that were fed a nitrogen-poor diet restricted their total activity while their mates sustained a high activity during colony initiation. When fed a nitrogen-rich diet, females collected pulp more often than their mates, while males collected more water, though only in the period prior to egg laying. In all pairs, males transferred proctodeal pellets (food derived from the hindgut intestine) to their mates significantly more often than females to males, and females fed on proctodeal pellets significantly more often than did their mates. The male-female asymmetries in pellet transfer and feeding were not significant in the stage after egg deposition. Once eggs and larvae were present in the nest, a male and female spend an equal percentage of time caring for eggs and feeding larvae. Proctodeal pellets examined in reproductives were found to be rich in proteins. This suggests that in the pre-egg period, the male provides nitrogen-rich substances to the female as a form of paternal investment.

The effects of heat shock and inoculum density on growth and sporulation in axenic cultures of the flax rust fungus

The number of mycelial colonies of Melampsora lini (Ehrenb.) Lév. was increased by a 2-h heat shock at 31 °C delivered 3 h after uredospores were seeded on a liquid medium at 17 ± 0.5 °C under axenic conditions. At 35–38 days from seeding, the ratio of the respective number of colonies in shock and nonshock treatments in 125-mL culture flasks was highest (7.5 to 22) at inoculum levels (1 to 4 × 103 uredospores cm−2) that yielded about 10 colonies per flask without heat shock; the ratio declined sharply at inoculum levels adjusted to yield either smaller or larger numbers of colonies per flask without heat shock. Sporulation (extinction at 458 nm) and protein per colony were positively correlated; were not directly affected by heat shock; were determined by colony number; increased to maxima as mean colony number per flask increased from 1 or less to from 10 to 100 in different experiments; and decreased at higher colony numbers per flask. The results indicate that heat shock promotes the initiation of colonies; that colony number determines the duration of logarithmic growth; and that increasing competition among individual colonies is the primary factor limiting growth and sporulation, whether or not the uredospore germlings are subjected to heat shock.

Effect of heat shock on protein synthesis in flax rust uredosporelings

In uredosporelings of Melampsora lini (Ehrenb.) Lév. germinated for 3 h, uptake of [35S]methionine and its incorporation into protein were depressed during a 2-h heat shock induced by transfer from 17 ± 0.5 to 31 °C. Spectrophotometric scans of fluorograms, prepared after one-dimensional sodium dodecyl sulphate – polyacrylamide gel electrophoresis of aliquots of protein extracts containing equal numbers of disintegrations per minute (1 dps = 1 Bq) in protein, showed that heat shock induced statistically significant changes in the relative degrees of incorporation of [35S]methionine into 15 polypeptide bands. Increased labelling occurred in seven bands, which appear to be heat shock proteins with apparent molecular masses of 84, 71, 43.5, 30.5, 19.5, 18, and 17 kD. Decreased labelling occurred in eight bands, which appear to be heat stroke proteins with apparent molecular masses of 56, 54, 48, 46, 34, 32, 31.5, and 14 kD. When [35S]methionine was administered during heat shock at 31 °C the same pattern of polypeptide labelling was observed in extracts made immediately without return to 17 °C and in extracts made after uredosporelings were returned to 17 °C for 24 h. Thus label incorporated into each polypeptide during heat shock was retained for at least 24 h after the return to 17 °C. Administration of [35S]methionine at 17 °C after completion of the heat shock showed that the "normal" or "nonshock" pattern of labelling began to be resumed within 2 h after transfer from 31 to 17 °C. The results are discussed in relation to the effect of heat shock in promoting the initiation and growth of mycelial colonies from uredosporelings in axenic culture.

Potentiation of anchorage-independent colony formation by sodium polyanethol sulphonate.

Sodium polyanethol sulphonate (SPS) when incorporated into rat erythrocyte lysate (REL) containing semi-solid agar medium at 1 mg ml-1. markedly enhanced colony formation by a number of anchorage-independent cell lines. REL usually needed to be included for the expression of SPS induced potentiation as in its absence SPS was generally cytotoxic. Studies suggested that SPS reduced the lag prior to colony initiation resulting in the earlier appearance of colonies and in a higher cloning efficiency. The effectiveness of SPS in potentiating colony formation by responsive cell lines was markedly influenced by the species of serum and to a lesser extent by differences between individual batches. Enhancement by SPS was greater with poorer foetal calf serum (FCS) batches than with better. This effect may have been partly due to SPS interfering with the action of a growth inhibiting serum component, possibly a lipoprotein. Studies in which delipidated FCS was substituted for normal FCS suggested that SPS was also able to compensate for the lack of a growth-promoting lipid component. Binding studies showed that initially 125I-SPS bound equally well at 4 degrees C and 37 degrees C with continued labelling occurring only at 37 degrees C. Autoradiography of cells labelled at 37 degrees C for 24 h revealed the presence of intracytoplasmic 125I-SPS.

Nest Architecture of Three Ropalidia Species (Hymenoptera: Vespidae) on Leyte Island, The Philippines

The nest of Ropalidia gregaria, R. horni, and R. flavopicta flavobrunnea are described in detail for the first time. Ropalidia gregaria and R. horni make uncovered nests with single combs. The nest of R. gregaria is round in shape and constructed on leaves, while that of R. horni is slender with a lobe-like projection at the base and constructed on twigs. On the other hand, comb formation of the covered nest of R. flavopicta flavobrunnea varies. Some nests show vespine-like comb formation while others show complex, subspiral structure. The heads of larvae and caps of cocoons of R. gregaria and R. horni are the same brownish color as nest materials. These characters probably help to make the nest less conspicuous in its particular surroundings. The nest of R. flavopicta flavobrunnea on a thick branch looks like a part of the tree. DESPITE THE FACT THAT THE GENUS Ropalidia consists of more than 100 species widely spread over the Ethiopian, Oriental, and Australian Regions (van der Vecht 1941, Richards 1971), little is known of the biology of these wasps. The genus is of considerable interest, as it includes both independent-founding species (one or several queens found colonies without workers) and swarm-founding species (colony is founded by a swarm of workers accompanying one or several queens) (Jeanne 1980a). The comparison of nesting behavior among the congeners may contribute to an understanding of the evolution of these two major modes of colony initiation. Likewise, comparison of the nest architecture can supplement phylogenetic studies at the specific or subgeneric level. In the present paper I describe the nest architecture of Ropalidia (Icariola) gregaria (Sauss.), Ropalidia (Icariola) horni Sonan, and Ropalidia (Icarielia) flavopicta flavobrunnea van der Vecht, based on 24 nests collected on Leyte Island, The Philippines, in March and April of 1978 and in June of 1980. The adaptiveness of the nest architecure is discussed in relation to the tropical environment, where there is high predation pressure on social wasps. Further, the nest of R. fla'vopicta flavobrunnea is compared with those of four consubgeneric members described by other authors. HABITAT AND SUBSTRATE All the nests but one (HT-01, collected at Tibuk) were collected or observed at Palo (110 09 N, 1250 01' E), located near the coast about 10 km south of Tacloban. Nests of R. flavopicta flavobrunnea were found mainly on thick branches of broad-leaved trees which invaded the coconut plantation surrounding the town. Nests were usually built well above the ground, mostly under the base of the first branch, excepting one found on the trunk of a coconut tree (table 1). Judging from the abundance of adults collected and nests discovered, this species is the commonest social wasp in the region. On the other hand, R. gregaria and R. horni nested in rather open places, such as roadsides and gardens (table 1). Ropalidia gregaria typically nested on the underside of leaves, while R. horni nested exclusively on twigs or branches. The plant species chosen for nesting and nesting height varied within each species. Ropalidia gregaria tended to prefer sunny places, while R. horni nested in shady places, such as bushes and lower branches of large trees.

The relation between worker numbers and the production of males and queens in the bumble bee Bombus perplexus

The first-brood worker populations of 18 artificially fed colonies of Bombus perplexus were adjusted to two, four, or eight and allowed to treble with the emergence of the second brood. The timing of male production was independent of the number of workers present and independent of the time of colony initiation. Consequently the duration of the premale period was correlated with the earliness of colony initiation. The first queens emerged after a mean delay of 3.2 days after the first males, this delay being shorter if more workers were present. The rate of pollen consumption per unit larval area was lower with only two workers present than when there were four or eight, but no association was found between the time of initiation of queen production and high ratios of worker numbers to larval area.

SEX RATIO COMPENSATION IN ANT POPULATIONS.

Forsyth (1981) has studied the sex ratio in colonies of the hymenopteran ant, Apterostigma dentigerum. Mating, colony initiation, and sexual production occur throughout the year, so that, at any time, a sample should reveal a typical cross-section of the population. Colonies are started by a queen who produces workers and reproductives. If the queen dies or fails to function, at least one worker will develop ovaries and lay (unfertilized) male eggs. Forsyth found that queens produced reproductives with a female-biased sex ratio. He suggested that this bias might have evolved to compensate for the all male production of workers in colonies which had lost their queen. My purpose is to build a simple model to see how such sex ratio compensation might work. Forsyth ascertained that male and female alates had the same dry weight, hence assumed that they were equally expensive to make, and that ratios of investment in the two sexes could be calculated by counting individuals. Of 53 colonies sampled containing sexual alates, 35 had a functional queen and had produced 269 female and 164 male alates, and the remaining 18 had no functional queen and had produced 121 males. The observed sex ratio of queen production is 164/433 = .38 males/total giving an overall population sex ratio of 285/554 = .51. To construct a simple model for this situation, let /3 denote the ratio of worker reproductive output to queen reproductive output in the population. Forsyth's estimate of /8 would be 121/433 = .279. Denote by r the equilibrium sex ratio (proportion of males) of queen produced offspring. In a steady state situation each queen expects to contribute to the next generation, 1 daughter, r/(l r) sons and ,B(1 + r/ (1 r)) = ,3/(1 r) grandsons (by a worker), and each male expects to mate with (1 r)/(/3 + r) queens. Following the standard ESS argument, we suppose the sex ratio r is controlled by an allele t which is expressed in the queen. We postulate a rare mutant allele T, dominant over t, which codes for an alternative ratio s. Then r is the equilibrium value if for every s $ r, the allele T has no selective advantage over t. The rarity of T allows us to ignore matings between Tt females and T males, and hence ignore the existence of TT females. If we denote by x and y the numbers of Tt queens and T males, respec-

CO2 is essential for colony initiation by flax rust fungus grown in vitro

Cultures were grown under a constant stream of gas of known composition to eliminate accumulation of any volatiles produced by the fungus. CO2-free air completely inhibits colony initiation. Air containing 1% CO2 allows colony initiation to the same extent as occurs in plugged, nonaerated controls, while "normal air" (ca. 0.03% CO2) causes initiation to be delayed to a variable extent.

Chapter 15 Serial Cultivation of Normal Human Epidermal Keratinocytes

This chapter discusses the serial cultivation of the normal human epidermal keratinocytes. Fibroblasts can be grown from almost any explanted human tissue and can be serially passaged and even cloned from low-density platings. Keratinocyte colonies are initiated by plating a single-cell suspension of keratinocytes with 3T3 feeder cells in the usual way such that less than 300 colonies arise. Newborn foreskin is a convenient source of human keratinocytes possessing a high-proliferative capacity in culture. Trypsin alone is sufficient to completely disaggregate this tissue to single cells with a yield of about 3 million cells per square centimeter of epidermal surface. The keratinocytes attach directly to the culture vessel surface and push away the 3T3 feeder cells as the colonies expand. In secondary and subsequent cultures, however, keratinocytes do not assume normal epithelioid morphology during the early stage of colony initiation in the absence of hydrocortisone, although colony-forming efficiency is unaffected. Cells growing in the absence of hydrocortisone eventually organize into normal colony morphology by the time colonies have reached a size of about 100 cells. The expression of tissue-specific structure and function by cultured keratinocytes is discussed in the chapter.

Colony initiation in flax rust in axenic culture: involvement of a volatile factor

In axenic cultures of flax rust (Melampsora lini) colonies are initiated after a lag period of 12–20 days, depending partly on incubation temperatures. Colony initiation is completely inhibited by removal of a volatile factor which is absorbed by KOH in the air space of the culture flask. The fungus remains sensitive to this inhibition for 8–10 days, i.e., until shortly before visible colonies would normally have developed. While in the presence of KOH, the fungus is not killed; cultures grow normally after removal of the KOH.Although conclusive evidence must await further work, the available data strongly suggest that carbon dioxide is responsible for this effect.

Oidaematophorus monodactylus as a Biocontrol Agent of Hedge Bindweed: Development of a Rearing Program and Cost Analysis12

Direct costs for rearing 10,000 3rd instars of Oidaematophorus monodactylus (L.) for field release to control hedge bindweed Convolvulus sepium L., in southwestern Virginia averaged 78¢/insect. This estimate was based on colony initiation by using field collected larvae in the summer, maintenance of a minimal population in the fall and winter, and subsequently increasing the population in spring for a June release of 3rd instars. Primary cost factors were labor, equipment, and materials; 30% were nonrecurring expenses.

Interactions of Puccinia hordei and Erysiphe graminis on seedling barley

SUMMARYThe development of Puccinia hordei on the first leaf of barley seedlings previously inoculated with Erysiphe graminis was compared with that on uninoculated leaves of comparable age. On cv. Zephyr, more rust pustules developed when leaves were inoculated with both fungi within 24 h but fewer pustules if the period between the two inoculations was longer than 2 days. The reduction in numbers of rust pustules was especially marked where leaves were previously inoculated with many conidia of E. graminis. The size of rust pustules was reduced whatever the period between the two inoculations. Arresting mildew development by applying ethirimol as a soil drench to pots of seedlings inoculated with E. graminis 6 days previously, or floating segments of leaves inoculated with both fungi on 2% sucrose, in part counteracted these effects on rust pustule size. Similar effects were observed with cv. Mazurka where inoculations with E. graminis produced only small necrotic flecks but did induce premature loss of chlorophyll. On this cultivar (in contrast to Zephyr) the inoculation of one leaf surface affected the development of P. hordei on the other.In comparable experiments using Zephyr, E. graminis produced smaller colonies with fewer conidiophores on leaves previously inoculated with P. hordei. These effects could be alleviated by arresting rust development with a spray containing benodanil or by floating segments of leaves inoculated with both fungi on 2% sucrose. Germination of the conidia of E. graminis, formation of appressoria and initiation of colonies were not affected by the presence of P. hordei.

The incipient stages of development of bumblebee colonies

In wild colonies ofBombus agrorum andB. hortorum initiation of the incipient brood clump preceded that of the honey-pot. In these, and other species, actual wax egg cells were not constructed but characteristic waxcovered brood clumps, containing eggs and pollen, were produced. Eggs of the first brood batch in natural colonies ofB. agrorum, B. humilis, B. pratorum andB. hortorum were deposited vertically.B. hortorum queens laid their eggs within the pollen lump, but inB. agrorum, B. humilis andB. pratorum, eggs were deposited against the pollen lump. In laboratory-initiated colonies, eggs were laid horizontally, often in actual wax egg cells. The order of colony initiation by captive queens did not always conform to that observed for the same species in the wild. In naturalB. agrorum andB. humilis colonies the arrangement of 8 eggs, larvae or pupae into a central row of 2 individuals, and two lateral rows of 3 individuals each, was typical.B. hortorum was more prolific, there usually being from 11 to 16 individuals in a brood clump, but no definite arrangement of eggs, larvae or pupae within brood clumps of this species was established. High brood mortality rates were not characteristic of the incipient stages of colony development in any species.

The portrayal of Africans in agricultural films of Southern Rhodesia (Zimbabwe): 1940s to 1950s

One of the most effective cultural tools used by the colonial governments in Africa to make their rule acceptable to African indigenous populations was film. In Rhodesia (now known as Zimbabwe) the colonial government created the Central Film Unit whose major aim was to teach Africans new agricultural methods. The response by Africans to this colonial initiative was mixed. Some welcomed and enjoyed the films and made use of the skills that the films popularised, but others were cynical and viewed these films as a tool to consolidate British white settler rule in Rhodesia. This article analyses six colonial films produced in the 1940s and 1950s. The article argues that through the use of colonial films, the Rhodesia government was able to persuade African communal farmers to adopt modern methods of farming. The irony of this is that the use of modern farming methods made it possible for the same colonial authorities to later blame Africans for the ecological disaster in the communal areas.

The cellular composition of hemopoietic spleen colonies

AbstractThe cellular composition of individual hemopoietic spleen colonies has been studied using techniques which tested primarily for cell function rather than cell morphology. Erythroblastic cells were recognized by their capacity to incorporate radioiron, granulocytic cells by their content of peroxidase‐positive material, and hemopoietic stem cells by their ability to form spleen colonies in irradiated hosts. It was found that, 14 days after the initiation of spleen colonies, the distribution of these cell types among individual colonies was very heterogeneous, but that most colonies contained detectable numbers of erythroblasts, granulocytes and colony‐forming cells. An appreciable proportion of the cells in the colonies could not be identified as any of these three cell types. No strong correlations between numbers of erythroblasts, granulocytes and colony‐forming cells in individual colonies were observed, though there was a tendency for colonies containing a high proportion of erythroblasts to contain a low proportion of granulocytes, and for colonies containing a high proportion of granulocytes to contain a higher proportion of colony‐forming cells. An analysis of colonies which contained cells bearing radiation‐induced chromosomal markers indicated that 83–98% of the dividing cells within 14‐day spleen colonies were derived from single precursors.

Bumblebee ecology in relation to the pollination of alfalfa and red clover

The ecology of bumblebees has been discussed under two major headings: (1) floral hosts and (2) populations. An understanding of the environmental factors that (1) affect the behavior of bumblebees in visiting flowers and (2) influence the production of a worker field force are basic to the utilisation of bumblebees in a practical way for the increased pollination, or more consistent pollination of alfalfa and red clover seed crops. Information is presented about the host plants in their seasonal succession, and the attractiveness of various flowers during the period of worker activity. Certain species of bumblebees are shown to differ in their preference of red clover and alfalfa. The initiation of colonies, the proper development of the brood, and the production of the workers have been related with ecological factors having major influence. Optimum conditions will be required for the culmination of a colony in a maximum force of worker bees at peak availability for pollination. Worker populations vary widely between species and among colonies of the same species. An elucidations of the reasons for the fluctuations will require additional biological and ecological research.

XXII.—The Autecology of Bracken (Pteridium aquilinum (L.) Kuhn): The Germination of the Spore, and the Development of the Prothallus and the Young Sporophyte

The rapid spread of bracken in some parts of the country has led to considerable investigation into the habits of the plant. But in almost all cases it is the spread of the adult sporophyte which has been described, and little attention has been paid to the insignificant, complementary half of the life cycle—the prothallus. Nor does any attempt appear to have been made to assess the rate of development of the prothallus and the young sporeling. A recent attempt to collect records of the occurrence of prothalli and young sporophytes in the field has shown how seldom they are found, and has emphasised the fact that little is known of the extent to which the plant spreads by the initiation of new colonies from spores (White, 1930).