236 COMPARATIVE MORPHOLOGY OF FUNGI 



spore form and connected with each other by transitional forms; still, 

 often depending on conditions, one or the other type predominates. The 

 microconidia are small, spherical or elongate and 1 to 2 celled (Fig. 

 150, D); they were earlier placed in the Imperfect genus Cephalosporium, 

 as they are collected into small heads. The macroconidia are larger 

 and often falcate; on account of this shape they were placed in the Imper- 

 fect genus Fusarium along with the conidia of many other Hypocreales. 

 They are mostly multiseptate, but under unfavorable conditions of 

 growth the septa may be subsequently dissolved or they may never be 

 formed. For the purpose of easier survey, these Fusaria important in 

 plant pathology have been grouped, according to form, size and septation, 

 into several types, as F. Solani, F. subulatum, F. discolor, F. gibbosum, F. 

 Willkommii and F. didymum (Fig. 151). 



The fructifications of the perfect form, the perithecia, arise generally 

 singly or in loose groups and rest loosely on the substrate or on a more or 

 less strongly developed subiculum (Fig. 151, B). In the forms with 

 Tubercularia stromata, they are laid down on or in these stromata (Fig. 

 152, B) and are then generally united in groups; they may often be found 

 singly, however, also on the same piece of bark, without stromatal 

 development. Their formation is preceded by the formation of a helical 

 ascogonium whose cells are multinucleate in the species so far studied, 

 Nectria Ribis, N. galligena and possibly N. Ipomoeae (Vincens, 1917; 

 Cayley, 1921; Cook, 1923); unfortunately more details of cytological 

 development are unknown. The perithecial rind is generally deeply 

 colored : in Nectria, Calonectria and Pleonectria, yellow, red or brown, in 

 age often almost black; in Gibberella brown or violet. Here also as in 

 the mycelial mats, however, the colors are frequently dependent on the 

 reaction of the substrate; thus the perithecia of G. Saubinetii are blue 

 on alkaline media, red to brown on acid. 



Systematically these four genera have, if possible, a larger variety of 

 forms than the Aspergillus- Penicillium group of the Plectascales, and 

 hence, up to .the present, have defied satisfactory solution (Appel and 

 Wollenweber, 1914). There is no doubt that in the principles of division 

 employed at present (of the forms with yellow or red perithecia, the 

 Didymosporae to Nectria, the Phragmosporae to Calonectria, the 

 Dictyosporae to Pleonectria, and of the forms with violet or blue peri- 

 thecia, the Phragmosporae to Gibberella), species from entirely different 

 developmental series, on the basis of these two chosen characters, are 

 placed together in artificial heterogenous genera; up to the present, how- 

 ever, these principles cannot be replaced by a better artificial or phylo- 

 genetic system. Theissen (1911) attempts for Nectria to utilize the 

 condition of the ascospore membrane (smooth spores to the Leiosporae, 

 longitudinally striate spores to the Rhabdosporae and verrucose spores to 

 the Cosmosporae). Wollenweber (1924) attempts to utilize the imperfect 



