The life history and morphology of Dicranophora fulva Schröt

Abstract

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.