In this article we will discuss about the modes of reproduction in pilobolus which belongs to class phycomycetes.
Like Mucor mucedo, its vegetative body is a much-branched coenocytic mycelium consisting of rather coarser white hyphae and containing multinucleate, granulated and vacuolated protoplasm. Some of the hyphae penetrate the substratum and draw nourishment therefrom.
Pilobolus reproduces both asexually and sexually.
Asexual reproduction takes place by means of sporangiospores. The modes of development of the sporangia, columella and the formation of spores agree closely with those of Mucor mucedo, but the structure of the sporangium represents a special modification of the Mucor type. The many-spored sporangium, instead of being spherical is somewhat flattened and the upper half of the sporangial wall is very much thickened.
The columella is rather small and somewhat conical in shape. The part of the sporangiophore just below the sporangium enlarges considerably to form a sub-sporangial vesicle which may be three to four times the diameter of the flattened sporangium. Numerous glistening drops of water appear on the surface of the vesicle and the lower part of the sporangiosphore.
When the sporangiophore is in a fully turgid condition, the sub-sporangial vesicle has been found to be sensitive to the directive influence of light. This stimulus causes curvature of the lower part of the sporangiophore, and the sporangium is directed towards the source of light.
The neck, i.e. the constricted portion between the sporangium and the sub-sporangial vesicle, undergoes softening and stretching and finally the turgidity of the vesicle reaches to such a degree that the neck ruptures and the entire sporangium, with mature spore, is blown off along with the watery contents of the vesicle towards the sources of light, without much scattering of aim, to a distance of several centimeters. Hence, it is known as pilobousgun.
The sporangia finally descend on the vegetation, adhere to it and are taken up by animals. The spores, only after passing out of their alimentary canals, are capable of germination and give rise to mycelia of this mould under favourable conditions.
Sexual reproduction takes place by the union of two isogametangia and their coenocytic contents, and resembles essential features of the sexual reproduction of Mucor mucedo. But, in this case, the gametangia are somewhat club-shaped and they meet in such a way that they resemble a pair of tongs.
A coenocytic zygospore is formed, by their union, at the point of contact, and it appears as a bud and occupies, as if, a terminal position. P. crystallius is heterothallic, and the formation of a zygospore is dependent upon the union of mycelia of two sexual strains, ( + ) and (-).
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