276 COMPARATIVE MORPHOLOGY OF FUNGI 



slender mycelium which cuts off oval conidia, either laterally or termi- 

 nally, and on certain media, develop fructifications similar to those of 

 Sporonema Platani. On other media they form the pycnia of Discula 

 Platani and later the fundaments of the perithecia of Gnomonia veneta. 



Therefore, the conidia of G. veneta may arise in not less than four 

 different types, three on the hyphae, which so far have only been observed 

 in pure cultures, then on leaves, without pycnia (Gloeosporium nervise- 

 quum) on branches in sori with less marked pycnia (Discula Platani) 

 and finally in dead leaves in black, occasionally many chambered pycnia 

 (Sporonema Platani). If one considers the scattered mycological 

 publications and the tendency of some authors to describe imperfect 

 stages, it is not surprising that G. veneta has 15 synonyms in the 

 literature. 



The imperfect forms of other pathogenic species show a polymor- 

 phism similar to that of G. veneta. G. erythrostoma (Apiognomonia 

 erythrostoma) a leaf spot of cherry, forms pycnia out of which the conidial 

 mass is pressed as a helical thread. Solitary, helical, multinucleate 

 ascogonia develop and fuse with a small antheridium. Nuclear migration 

 occurs and the ascogenous hyphae of the hook type develop in the normal 

 manner (Brooks, 1910; Likhite, 1926). 



Gnomonia leptostyla, the anthracnose of walnuts, has only free conidio- 

 phores which sometimes in the same sorus, but more often separately, 

 cut off at the pointed end, fusarioid macroconidia (Marssonina Juglandis) 

 and smaller, unicellular bacilliform microconidia (Leptothyrium Juglandis) . 

 The young antheridia and ascogonia develop in the degenerate par- 

 enchyma. The antheridia are unicellular and multinucleate. They fuse 

 with the ascogonia and degenerate, while the ascogonia continue to develop, 

 putting forth on all sides, short protuberances from which the asci 

 develop directly, as in the Plicaria succosa type (Likhite, 1926). 



Ophiobolus has long slender ascospores which often separate into their 

 individual cells. Its best-known species is 0. cariceti (0. graminis, 0. 

 herpotrichus) , the cause of take-all of wheat and other cereals (Kirby, 

 1924). Imperfect forms have not yet been reported. The mycelium is 

 uninucleate and intracellular, capable of penetrating cells without 

 developing haustoria. At the beginning of spermagonial formation, 

 the tips of a number of hyphae congregate and, by further growth and 

 intertwining, form a loose ball of hyphae. This expands and the outer 

 layer becomes increasingly pseudoparenchymatous. The cavity is 

 bounded by a layer of uninucleate, pyriform cells with their narrow ends 

 toward the center of the cavity. They give rise to short, narrow cells 

 of varying length which abstrict the bacilliform spermatia from their tips. 

 The spermatia are sometimes arranged in short chains but are no longer 

 functional. Their nuclei are very large and they are completely devoid 

 of reserve material. 



