Dichotomous System Research Articles

The life history and morphology of Dicranophora fulva Schröt

Summary 1. Dicranophora fulva grows readily in culture, but forms no zygospores on purely artificial media. It is extremely sensitive to light, forming sporangia only when illuminated, and zygospores only in the dark, or in very diffuse daylight. 2. In the material studied, the columella in the large sporangium is rounded, not conical. There is a columella in the sporangiole, but the claw-like outgrowths described by previous authors have been observed only once. The columella in both large and small sporangia has, however, been seen to produce a hypha. 3. The reported dimorphism of the spores in the two sorts of sporangia does not exist, except in so far as the spores in the sporangiole are somewhat more compressed. The liberation of the contents of a large sporangium as a single giant spore is described. The range of spore size appears to be far greater than in any other Mucorales. 4. The sporangiole differs from the sporangium only in its size and position on a dichotomous branch system. Intermediate forms occur which are not distinguishable as one or the other. 5. The sporangiophore appears to give rise to about the same number of spores, whether it bears one large sporangium, or forms a branch system bearing many sporangioles. 6. Dicranophora is the only Zygomycete in which a constant size difference between the gametangia has been shown. It is unique in possessing a female organ which may have an independent existence apart from sexual contact, and it differs from most of the Mucorales in that the sexual branches grow into contact, and are not necessarily in contact from the first. 7. The extent to which the female branch produces an outgrowth towards the male is very variable. The wall between the gametangia breaks down before the larger one is completely isolated, and the whole contents of the male pass into the female gametangium, in which the zygospore is formed. 8. The zygospore is not spherical, but slightly flattened on one side, with a deeply creviced outer coat, and a small boss representing the male gametangium. It has not been germinated. Some abnormal zygospores are described. 9. Support is given to the view that Dicranophora should be classified with Sporodinia and Spinellus , rather than with Thamnidium . Certain marked resemblances to the Oomycetes are also pointed out.

IX.—A Critical Examination of the Vittarieæ with a View to their Systematic Comparison

The Vittarieæ, as described by Christensen, comprises five genera, viz. Vittaria, Monogramma, Antrophyum, Hecistopteris, and Anetium, all of which are epiphytic forms growing in the damp forests of the Old and New World Tropics. All of them possess creeping rhizomes on which the fronds are arranged more or less definitely in two rows on the dorsal surface. The fronds are simple in outline, with the exception of those of Hecistopteris which are dichotomously branched. The venation of the fronds is reticulate, except in Hecistopteris where there is an open, dichotomous system of veins, and in Monogramma, in some species of which the venation consists simply of a mid-rib. An interesting feature, which has proved to be valuable as a diagnostic character, is the presence of “spicule cells” in the epidermis of the fronds. These spicule cells are elongated cells containing spicules of silica, and their presence appears to be universal in the Vittarieæ. The sporangia are fairly constant in form through-out the group, but their distribution is extremely varied. The roots are characteristically provided with very numerous reddish-brown root hairs, a character shared with other epiphytic Ferns. The Gametophyte is divergent from the common cordate type in all cases where it has been investigated. Such are the main external characteristics of the group under consideration.

XXXII. On the dying struggle of the dichotomous system

XXXII. <i>On the dying struggle of the dichotomous system</i>

XX. On the dying struggle of the dichotomous system. In a Letter to N. A. Vigors, Esq. F.R.S.

XX. <i>On the dying struggle of the dichotomous system. In a Letter to</i> N. A. V<scp>igors</scp>, <i>Esq. F.R.S.</i>

XI. On the dying struggle of the Dichotomous System

XI. <i>On the dying struggle of the Dichotomous System</i>

LXII. On the dying struggle of the dichotomous system

(1830). LXII. On the dying struggle of the dichotomous system. The Philosophical Magazine: Vol. 7, No. 42, pp. 431-445.