SECT. I 



CRYPTOGAMS 



349 



a single spore, as the result of certain conditions of food-supply, and in this way 



assume the character of conidia. This dimorphism is even more complete in the 



tropical genus Choanephora, found on 



the flowers of Sibiscus. In this case, 



in addition to large sporangia, conidia 



are produced on special conidiophores. 



There are, finally, Zygomycetes (e.g. 



Chaetocladium) whose only asexual 



spores are conidia. In this one group 



of the Hyphomycetes, therefore, all 



transitional forms, from many-spored 



sporangia to unicellular conidia, are 



represented. 



The genus PUdbolus, frequently 

 found on dung, possesses a, special 

 contrivance for the dissemination of 

 its spores, which are formed, like those 

 of Mueor, in large terminal sporangia. 

 The stalk of the sporangiophore, imme- 

 diately below the sporangium, becomes 

 swollen and pear-shaped : in conse- 

 quence of the increased turgor result- 

 ing from the absorption of water, the 

 columella finally bursts, and the liquid 

 which is thus set free tears loose the 

 sporangium and discharges it, with 

 great force, to a considerable distance. 

 The sporangiophores of Pilobolus, and 

 also those of other Mucorineae, are dis- 

 tinctly positively heliotropic (p. 252). 

 For physiological experiments Phyco- 

 myces nitens is also largely used. Its 

 sporangiophores are constructed simi- 

 larly to those oiMucorlfucedo, but attain 

 a very much greater length (10-30 cm. ). 



Sub-Class 3. Hemiasei 



Fig. 271. — Mucor Mucedo. Different stages in 

 the formation and germination of the zygo- 

 spore. 1, Two conjugating branches in con- 

 tact ; 2, septation of the conjugating cells (o) 

 from the suspensors (b) ; 3, more advanced stage 

 in the development of the conjugating cells (a) ; 



4, ripe zygospore (b) between the suspensors (a) ; 



5, germinating zygospore with a germ - tube 

 bearing a sporangium. (After Brefeld, 1-4 x 

 225, 5 x circa 60.) 



This group includes only a few small Fungi with a septate mycelium, 

 which, as in all the higher Fungi, develops no sexual organs. Asexual 

 reproduction is effected by means of ascus-like sporangia, which, although 

 they show a certain resemblance to the asci of the Ascomycetes, do not 

 produce a fixed number of spores of definite form and size. 



Protoinyces pachydermus, parasitic upon Cichoraceae, may be cited as a typical 

 Fungus of this class. In addition to sporangia it produces accessory fructifications 

 in the form of conidia and chlamydospores (p. 34#). The last named are formed 

 from the mycelium ramifying in the tissue of the host-plant, by the spherical 

 enlargement of chains of hyphal cells whose walls become thickened (Fig. 272, 

 1). The germ -tubes arising from the germinating chlamydospores become 

 converted directly into saccate sporangia (2, 3) by the division of their proto- 



