424 COMPARATIVE MORPHOLOGY OF FUNGI 



This acquires greater probability from the numerous examples in which 

 the nuclear number still remains eight or four while the spore number is 

 smaller. 



A similar origin for the chiastobasidium may be proposed. Trans- 

 verse nuclear spindles often appear in the first division of the primary 

 ascus nucleus, as we have shown in Taphrina and Podospora (Figs. 102, 

 3 and 6; 174, 3); in Hydnobolites of the Tuberaceae they lie just below 

 the tip of the ascus. By similar considerations, spore formation would 

 then be transferred from the interior of the ascus to the outer surface, 

 and the spore number would be reduced from eight to four and two; 

 thus the chiastobasidium might be considered an ascus with exogenous 

 spore formation. Maire (1902) suggested that the stichobasidium had 

 been transformed in different parts of the system to chiastobasidium, 

 and in the main builds his phylogeny of the Basidiomycetes accordingly. 

 It is difficult to see what reasons he had for this transposition. The 

 longitudinal nuclear division is undoubtedly freer and a transverse 

 position of the nuclear spindles may be explained, especially where it 

 is connected (as in Vuilleminia) with a marked broadening of the basidial 

 tip, only by a phylogenetic limitation reaching far backward, not by a 

 casually appearing arbitrary fluctuation. Furthermore Juel (1898) 

 suggested the possibility that the chiastobasidium may have proceeded 

 from the TremeUa basidium, by loss of the septa. On the other hand, 

 Juel (1916) has called attention to the fact that the eight-spored chiasto- 

 basidium could not be explained in this manner (as the TremeUa basidium 

 is four-spored) and he proceeded to consider the chiastobasidial forms 

 as a separate line. 



The derivation of the phragmobasidium appears considerably more 

 difficult than the derivation of the autobasidium from the ascus. A 

 sentence of Maire (1902) appears to "hit the nail on the head," if one 

 substitutes phragmobasidium for ascus: "La baside, a peine eclose de 

 Uasque s'essaie pour ainsi dire dans diverses directions avant de prendre 

 un type definitif et constant;" in other words, the ascus which has developed 

 in the form of an eight-spored sporangium from the Protoascineae into its 

 character as gonocont, has again relaxed from an inflexible form; it came 

 again into a state of flux and transferred its spore formation from its 

 interior to its surface. As in the Mucoraceae, the development of these 

 does not remain stationary but proceeds, favored by the labile condition 

 of the primitive basidium, in different directions; this divergence of the 

 direction of development appears all the more natural since the possi- 

 bilities of development for a conidiophore are far more varied than for a 

 sporangium. 



We do not know what factors were decisive in this septation ; perhaps 

 the type of spore discharge contributed. Similarly, it remains an open 

 question whether this septation has appeared already at the ascus stage 



