200 COMPARATIVE MORPHOLOGY OF FUNGI 



thick hypha which in P. corylea, and in the forms of Erysiphe Polygoni 

 (E. communis) on Ranunculus acris investigated by Dangeard includes, in a 

 manner still unexplained, several bi- and several uninucleate cells; in the 

 form of E. Polygoni on Leguminosae investigated by Harper, septation is 

 first absent apparently because of very rapid elongation (Fig. 125,1), 

 so that the hyphae have five to eight nuclei and only subsequently divide 

 into single cells; thereby the subterminal cell is binucleate (Fig. 126, 6 and 

 7). The relationships are difficult to follow cytologically, as the copula- 

 tion branches are already surrounded by a thick hyphal knot into which 

 the primary ascogenous hyphae, growing out from the ascogonium, 

 penetrate with irregular twistings. In a manner still to be studied, one or 

 more of the binucleate cells grow out of this primary ascogenous hypha 

 to secondary ascogenous hyphae (Fig. 126, 8 and 9) which branch many 

 times, and change the terminal cells to asci with nuclear fusion. 



In Sphaerotheca, alone of all the forms so far studied, the primary 

 ascogenous hypha, itself growing from the ascogonium, proceeds directly 

 to the formation of a single ascus. Thus, as in Erysiphe Polygoni 

 the ascogonium develops to a multinucleate tube which divides simul- 

 taneously into several uninucleate cells and a subterminal binucleate cell 

 (Fig. 124, 6). This subterminal cell develops directly to an ascus, with 

 the fusion of its dicaryon. While each of the perithecia in the first type 

 includes several (up to 20) asci, in the Sphaerotheca type it contains only 

 one. In both, the primary ascus nucleus undergoes three steps in divi- 

 sion, whereupon the daughter nuclei cut out of the protoplasm eight (or, on 

 account of abortion, only four or two) unicellular, later brown ascospores. 

 These, probably the largest unicellular spores in the fungi, in Phyllactinia r 

 corylea attain a length of over 50 ju. They are liberated by irregular 

 rupture or by crumbling of the peridium. 



An interpretation of the relationships of the first and second types of 

 development seems to be possible only on the basis of relationships 

 described in the Plectascales. The first type (Phyllactinia-Erysiphe) may 

 be directly referred to the Aphanoascus-Penicillium type, in which the 

 ascogenous hyphae divide into two phases of which only the second is 

 sporogenous. Only in the Phyllactinia-Erysiphe type, and this seems to 

 be a new character for the group, the first phase undergoes a gradual 

 degeneration, while in Phyllactinia corylea and in Erysiphe Polygoni 

 (E. Martii), as in the Plectascales, several binucleate cells are formed in 

 the first phase so that several ascogenous hyphae result. There is only 

 one binucleate cell in the form of Erysiphe Polygoni (E. communis) 

 studied by Harper, consequently the number of ascogenous hyphae is 

 limited to a single one which, by branching considerably, gives rise to a 

 few asci. 



This limited elongation in the first phase of the ascogenous hyphae 

 may undoubtedly be called the new characteristic point of the Erysipha- 



