PHYCOMYCETES.— (^) ZYGOMYCETES 



425 



these parasites the sporangiopliores are profusely branched, and tliey boar 

 many unicellular, conidiuni-like bodies, easily detached, and carried by the 

 wind. That they are really sporangia of very reduced form is indicated by 

 intermediate types, with niinute sporangia, which contain a few spores. Even 

 Mucor itself, when star\'ed, ma}' produce such small sporangia, which show how 

 the still simpler condition may arise. The family thus illustrates a transition 

 from water-dispersal, by spores produced internally in lew large sporangia, to 

 dispersal through the air of sporangia reduced to a single cell, and produced 

 in larger numbers. The latter may be held as a derivative condition. 



A very peculiar mode of dispersal is by forcible projection of the whole 

 sporangial head. This is seen in Pilobolus, whence its name. The sporangium 

 is constructed like that of Muoor ; but at ripeness it breaks away from the 



C .; 



^ 



^^^.^ 



Fig. 360. 



I, Mucor nutcedo, a sporangium in optical longitudinal section. c=columella. 



»i — wall of sporangium. s/> = spores. 2. Mucor miictlagineus, a sporangium shedding 



its spores ; the wall (m) is ruptured, and the mucilaginous matri.x (r) is greatly 



swollen. (After Brefeld. i x 225 ; 2 x 300, after v. Tavel.) (From Strasburger.) 



stalk, which has become turgid with sap under osmotic pressure. By the 

 principle of the squirt this fluid is thrown out to a distance of some inches, 

 carrying mth it the sporangial head. A similar projection happens in 

 Empusa, but here it is only a single conidium that is discharged, which, adhering 

 to any sohd body, causes the halo previously mentioned. There is thus a 

 considerable variety in the methods of dissemination in the Zygomycetes. 



The spores of many of the Mucorineae contain more than one 

 nucleus. There are said to be two in Pilobolus, and many in 

 Sporodinia. In the latter, which grows parasitically on large sapro- 

 phytic species of Boletus, the sporangial head is first shut off by a 

 septum : this becomes convex, and forms the central columella. 

 The large poly-nucleate mass of protoplasm filling the head then 

 undergoes cleavage into a number of parts, each containing several 

 nuclei. These rounding themselves off form the spores. Such 

 cleavage of the contents of the sporangium is the typical method of 

 formation of spores in the Mucorini. The final result is the same in 

 all : viz. germination under favourable circumstances to form a new 

 non-septate, and poly-nucleate mycelium. 



