Micropylar Haustorium Research Articles

Embryology of Mimulus Ringens

The wall of the microsporangium in Mimulus ringens L. consists of an epidermis, endothecium, middle layer, and glandular tapetum. The tapetal cells become binucleate, and the endothecial cells develop fibrous thickenings in later stages. Division of microspore mother cells is simultaneous, and quadripartition takes place by cleavage. The pollen grains are two-celled at shedding. Development of the female gametophyte in the tenuinucellate hemianatropous ovules conforms to the Polygonum type. Two superposed persistent antipodal cells are organized, the more micropylar cell being larger and binucleate. An endothelium surrounds the central portion of the embryo sac. The endosperm is ab initio cellular. A chalazal haustorium, which consists of four uninucleate cells, becomes conspicuous only after degeneration of the antipodal cells. A micropylar haustorium, made up of two large binucleate cells, also occurs. The haustorial cells do not fuse but degenerate as such. Development of the embryo conforms to the typ...

Studies of Floral Morphology in the Ericales VII. Embryology in the Phyllodoceae

Various aspects of embryology have been described for 16 taxa representing six genera of the tribe Phyllodoceae (subfamily Rhododendroideae, family Ericaceae): Daboecia cantabrica, Kalmia angustifolia, K. hirsuta, K. latifolia, K. polifolia, K polifolia var. microphylla, Leiophyllum buxifolium, L lyoni, Loiseleuria procumbens, Phyllodoce aleutica, P breweri, P caerulea, P empetriformis, P. glandulifiora, P. nipponica, and Rhodothamnus leachianus. The flowers are actinomorphic, bisexual, and hypogynous. They are pentacyclic except in Loiseleuria, sympetalous except in Leiophullum, and pentamerous except in Daboecia which is regularly, and Rhodothamnus which is occasionally, tetramerous and in Leiophyllum and Loiseleuria in which the carpel number is reduced to two or three. The stamens are obdiplostemonous and unappendaged, the anthers inverted to an introrse position. There are four microsporangia; the two in each anther half become confluent at maturity. The anther has an epidermis, two to three wall layers, and a glandular tapetum whose cells become more than one-nucleate. Dehiscence is accomplished by resorption tissue, but, in addition, a local endothecium occurs in Kalmia, Phyllodoce, and Rhodothamnus. The region of dehiscence is a short slit in Kalmia, Phyllodoce, and Rhodothamnus, a broad pore in Daboecia, or a longitudinal slit extending the whole length of the anther in Leiophyllum and Loiseleuria. Following meiosis in the microspore mother cells, cytokinesis by furrowing is simultaneous. The tetrads, commonly tetrahedral but occasionally decussate, do not separate to their component spores. Each cell of the compound pollen grain is binucleate with a large vegetative and a small generative nucleus. The ovules, which range in number from 40 to more than 180 per carpel, are anatropous to slightly campylotropous and are borne on placentation which is axile in the base and becomes parietal in the upper part of the ovary. They are unitegmic, the integument of varying thickness, and tenuinucellate. The innermost layer of the integument differentiates as an endothelium. A single archesporial cell becomes the megaspore mother cell directly. Meiosis results in a linear tetrad (rarely ⊤ or ⊥), of which the chalazal spore normally functions to give arise to an eight-nucleate gametophyte. Development thus corresponds to the Polvgonum type. Following disintegration of the nucellus, the gametophyte penetrates into the micropyle so that the endothelium surrounds only its chalazal portion. The synergids are elongated in most species but short in a few. The polar nuclei fuse to form the secondary nucleus before fertilization. The antipodal cells are normally arranged in a ⊤, but in a few species are linear or both linear and ⊤. A few species have lateral protrusions near the egg apparatus. Pollen tube penetration is porogamous. Development of the endosperm is cellular and precedes that of the embryo. The first two divisions are transverse resulting in a linear row of four cells. The latter divide longitudinally forming four tiers of two cells each. The terminal cells form haustoria, while the central cells form the endosperm proper. The micropylar haustorium develops more rapidly and, except in Daboecia, more extensively, than the chalazal. The zygote elongates before undergoing the first division, which is transverse. The short terminal cell divides transversely to form two cells. The basal cell of the two-celled proembryo forms a suspensor, while derivatives of the terminal cell produce the straight embryo. Embryogeny conforms to the Solanad type of development. The seed is albuminous only the outermost layer of the integument persists, except in Daboecia where the hypodermal layer is also present. The inner two or three layers of the pericarp become sderenchymatous. In some fruits of Phyliodoce empetriformis thick-walled hairs grow from the inner epidermis of ovary wall and septa. They fill the locules and often enter the empty seeds Comparison of the organographical and embryological traits of the Phyllodoceae with those of other members of the Ericaceae and of other families of the Ericales supports the close affinity of the Phyllodoceae to the family and adds further corroboration to the existence of a peculiar battery of embryological features characterizing the order. For this tribe, however, embryological characteristics did not prove to be particularly useful in distinguishing genera; Daboecia is the only genus distinct embryologically

Contribution to the embryology ofChaenorrhinum Minus (L.) Lange

The paper reports on an embryological investigation ofChaenorrhinum minus. The development of the female gametophyte is of the Polygonum type. The antipodal cells degenerate early. The endosperm isab initio cellular. The chalazal haustorium is unicellular and binucleate, although occasionally a uninucleate state occurs. No micropylar haustorium is organized. The persistent, thick-walled endothelial cells contribute to the 4–5-layered seed coat. The findings have been evaluated in the light of previous work on the tribe Antirrhineae.

EMBRYOLOGICAL STUDIES IN CANADIAN REPRESENTATIVES OF THE TRIBE RHINANTHEAE, SCROPHULARIACEAE

Descriptions are given of the ovary and ovules, megasporogenesis, embryo sac, endosperm, embryo, and seed coat structure of Euphrasia arctica Lange, Orthocarpus luteus Nutt., and Melampyrum lineare Desr. Although the ovary is usually bicarpellary, syncarpous, and bilocular with axile placentation in the tribe, a tendency toward unilocularity and parietal placentation occurs in Orthocarpus luteus. The number of ovules is reduced to four in Melampyrum lineare. Development of the embryo sac is of the monosporic eight-nucleate type in Euphrasia arctica and Orthocarpus luteus, but is tetrasporic and seven-nucleate in Melampyrum lineare. No fusion of polar nuclei occurs in the latter. The endosperm is ab initio cellular. Nuclear division in the primary micropylar chamber is followed by a vertical wall which remains incomplete. Aggressive haustoria develop at opposite ends of the endosperm. The chalazal haustorium is unicellular and binucleate. The micropylar haustorium is incompletely bicelled, with four nuclei in E. arctica and M. lineare and two nuclei in O. luteus. In M. lineare six to eight tube-like processes develop from the micropylar haustorium of which one usually enlarges and enters the funicle. The endosperm proper is generally uniform in E. arctica and O. luteus, but in M. lineare it becomes differentiated into three regions, the massive micropylar part consisting of cells with thickened, prominently pitted walls and the chalazal part of thin-walled cells with large intercellular spaces. Embryo development in E. arctica and O. luteus resembles that of Capsella bursa-pastoris, while development in M. lineare follows that of Polygonum persicaria. Embryologically Melampyrum lineare differs markedly from other members of the tribe.

Embryology of Klugia notoniana

1. The anther wall of Klugia notoniana A.DC. consists of three layers of cells external to the glandular tapetum. The tapetal cells become binucleate or trinucleate, and the nuclei often fuse. The endothecium develops fibrous thickenings. Quadripartition of the microspore mother cells is simultaneous. The mature pollen grains are bicelled and triporate. 2. The ovules are anatropous, unitegmic, and tenuinucellate. Development of the embryo sac conforms to the Polygonum type. Two megaspore mother cells and megaspore tetrads have been found. 3. Double fertilization has been observed. 4. The endosperm is ab initio cellular. The chalazal haustorium is binucleate to start with but becomes uninucleate and very aggressive. The micropylar haustorium consists of two uninucleate cells and is active only during the later stages of seed development. 5. Development of the embryo conforms to that of Capsella bursa-pastoris.

SEED DEVELOPMENT IN ADHATODA VASICA NEES

The events following fertilization up to the maturation of the seed in Adhatoda vasica have been described. The first two transverse divisions accompanying the division of the primary endosperm nucleus partition the embryo sac into (1) a micropylar chamber, (2) a chalazal chamber, and (3) a central endosperm chamber. The first two develop into binucleate haustorial structures, while the bulk of the endosperm is derived from the products of the central endosperm chamber. An unusual case of a micropylar haustorium containing four hypertrophied nuclei and four small nuclei has been observed. The central endosperm chamber is partly cellular and bears a tubular free nuclear basal apparatus. The latter, however, ultimately becomes cellular. The embryo development is of the Solanad type. The mature seed has only two layers of thin-walled endosperm cells and a wavy testa representing the persistent epidermis of the integument. The rest of the integument is consumed by the endosperm. The uneven surface of the testa results from unequal development of the integumentary parenchyma and not due to either unequal radial stretching of the epidermis or irregular growth of the endosperm as in Andrographis serpyllifolia.

THE DEVELOPMENT OF THE SEED IN ANDROGRAPHIS SERPYLLIFOLIA

Mohan Ram, H. Y. (U. Delhi, India.) The development of the seed in Andrographis serpyllifolia. Amer. Jour. Bot. 47(3) : 215—219. Illus. 1960.–Andrographis serpyllifolia, a member of the Acanthaceae, has an embryo sac with a bifurcated chalazal part. At the time of fertilization both synergids and antipodal cells disintegrate. Early in its development the endosperm is composed of 3 distinct parts: (1) a binucleate densely cytoplasmic chalazal haustorium; (2) a large binucleate micropylar haustorium; and (3) a central chamber which develops into the endosperm proper. The divisions in the central endosperm chamber are ab initio cellular. A few of the endosperm cells elongate enormously, ramify into the integument and destroy the surrounding cells. These cells have been termed secondary haustoria. Due to the unequal destruction of the integument, the endosperm assumes a ruminate condition. The mature seed is nearly naked because the seed coat is almost completely digested. The embryo has a long suspensor. The micropylar cells of the suspensor are hypertrophied and multinucleate. Contrary to Mauritzon's (1934) belief, the course of endosperm development is markedly different from that observed in Thunbergia. So far, albuminous seeds have been reported only in the subfamily Nelsonioideae. The present investigation provides a case of its occurrence in the Acanthoideae also.

Contribution to the morphology ofPedalium murex Linn. andSesamum indicum D.C.

The development of microsporangium inPedalium murex Linn., is of the normal type. The cells of the primary sporogenous layer function directly as the pollen mother cells. The tapetum is multi-nucleate and exhibits nuclear fusion, prior to disintegration. InSesamum andPedalium the embryo-sac development conforms to the normal type. Chalazal nutritive tissue is met with inPedaliuin, while it is absent inSesamum. Endosperm is cellular. The occurrence of chalazal endosperm haustoria is reported in both the genera. No micropylar haustorium was observed. The chalazal haustorium is single celled and four nucleate inPedalium, while it is made up of two bi-nucleate cells isSesamum. The diploid chromosome numbers ofPedalium murex andMartynia diandra have been determined for the first time to be sixteen and thirty-two respectively. In the case ofPedalium the number is confirmed from meiotic counts also which shown=8.

Microsporogenesis and Development of Seed in Lobelia cardinalis

1. Each theca of the anther of Lobelia cardinalis contains many microspore mother cells. The tapetal cells are first uninucleate, later becoming binucleate. 2. Cell plates are formed on the cytoplasmic strands midway between the nuclei of the tetrad. 3. The generative cell divides to form two male gamete cells before the pollen grain leaves the anther. 4. Each carpel of the two-loculed pistil contains many ovules, which are anatropous at maturity. 5. Prior to the formation of the single integument, a single archesporial cell is found in the hypodermal layer of the ovule and functions as the megaspore mother cell. 6. Seven pairs of chromosomes are present at meiosis. 7. A linear row of four megaspores is formed, and the larger spore toward the chalazal end of the ovule is the functional megaspore which develops into an eight-nucleate seven-celled megagametophyte; the other megaspores disintegrate. The cells of the nucellus toward the micropylar end of the ovule disintegrate upon division of the nucleus of the megaspore. 8. A vascular strand is differentiated early in the development of the ovule and extends part way into the base of the funiculus. Conductive tissue extends from the vascular strand to the nutritive tissue at the chalazal end of the megagametophyte. 9. Double fertilization occurs. At metaphase in the first division of the endosperm nucleus the chromosomes of the endosperm nucleus and those of the male gamete nucleus move independently toward the mid-plane of the spindle. A four-celled endosperm is formed prior to division of the zygote nucleus. 10. The synergids and the antipodals function as chalazal and micropylar haustoria, respectively. The synergids become greatly enlarged and digest the cells of the integument about the micropyle. The nucellar cells at the chalazal end of the megagametophyte are digested by the antipodals, which later digest the cells of the adjoining nutritive tissue.

Cyto-morphological studies inAsteracantha longifolia nees. (Hygrophila spinosa. T. and.)

The haploid and diploid chromosome numbers ofAsteracantha longifolia Nees., are 16 and 32 respectively. The floral parts develop in the order calyx, andrœcium, corolla, and gynœcium. The anatomy of the stem, root and leaf and the morphology of the thorns have been described. The development of the micro- and megaspores is traced. In the embryo development suspensor haustorium and micropylar endosperm haustorium have been observed. The endosperm is cellular and the micropylar haustorium is bi-nucleate. The morphology of the jaculator is described. In regard to the position of the genus in the family correlation between Hobein’s classification on the basis of cystolith features and the chromosome numbers is suggested.

A Contribution to the Life History of Impatiens sultani

1. The ovule possesses but one hypodermal archesporial cell. 2. The archesporial cell is also the megaspore mother cell. 3. An axial row of two cells is formed. The chalazal cell is the mother of the embryo sac. 4. A normal 8-nucleate sac is formed. 5. There is a variation in the position of the synergid nuclei, due to their age. 6. The two polar nuclei come in contact directly beneath the egg and do not fuse until after the pollen tube has entered the embryo sac. 7. The 3 antipodals may be either 3 cells or a group of 3 nuclei cut off from the upper region of the sac by a membrane. 8. The antipodals disappear soon after the egg apparatus is formed. 9. The megaspore mother cell and the early 2-nucleate embryo sac are bounded at the apex and sides by the nucellar epidermis. 10. The embryo sac absorbs the nucellar epidermis and by means of an antipodal haustorium absorbs all of the nucellus between the sac and the chalaza. 11. The tapetum is derived from the inner layer of the inner integument. 12. The outer integument arises from the inner integument. 13. Binucleate tapetal cells surround the microspore mother cells. They also extend into the mass of sporogenous cells and separate the functional mother cells into groups. 14. The nucleus of the generative cell of the pollen grain apparently does not divide before pollination. 5. The pollen tube enters the embryo sac along the side of the filiform apparatus and extends down one side of the embryo sacuntil it is near the egg nucleus. 16. Two coiled sperm nuclei are often seen near the egg nucleus. 17. It seems very probable that triple fusion occurs. 18. An extensive micropylar haustorium and a more simple chalazal one develop from the endosperm. 19. The embryo possesses a short suspensor. 20. The bivalent chromosomes in both megasporogenesis and microsporogenesis show X's, Y's, and V's. 21. A multipolar spindle appears in the prophase of the heterotypic division in microsporogenesis. 22. The nucleus of the microspore has but a short period of rest; the prophase of division is initiated early and persists for some time.

The Embryo Sac and Embryo of Striga lutea

1. Striga lutea is a semi-parasitic annual belonging to the Rhinantheae-Gerardieae group of the Scrophulariaceae. 2. The ovary is of the ordinary bilocular scrophulariaceous type, and the ovules are anatropous, with one integument. 3. The megaspore mother cell arises directly from a single subepidermal cell, which gives rise to a row of four megaspores, of which the lowest develops into the embryo sac. 4. The 8-nucleate embryo sac develops in the normal way, and at the time of fertilization contains two synergids, an egg, the fused polar nuclei, which lie in the upper part of the sac, and three antipodal cells, which show signs of disintegrating. 5. Double fertilization occurs. 6. Endosperm is formed by cell division. From the chalazal end a long binucleate haustorium is formed, penetrating the integument. The micropylar haustorium is inconspicuous, simply consisting of a few ordinary endosperm cells with fairly dense contents. 7. The proembryo has a long suspensor of three or four cells. The basal cell of the suspensor forms tuberous haustoria. 8. The mature embryo is of the usual dicotyledonous type and is surrounded by one thick-walled layer of endosperm cells. 9. The testa consists of one layer of lignified cells which are admirably suited to protect the young embryo.