126 ASCOMYCETES AND RHODOPHYCE^:. 



Lastly, the development of the gonemoblast filaments in such forms 

 as Batrachospermum and Nemalion is certainly paralleled in the 

 ascogenous hyphae of Erysiphe, and for the same reason we may look 

 upon the ascogenous hyphae of Pyronema and Ascobolus as homolo- 

 gous with the sporogenous filaments of Dasya and Dudresnya. The 

 ascogenous hyphae obtain food later in their development from con- 

 tiguous vegetative cells existing chiefly for that purpose. In this case 

 a cytoplasmic fusion is not necessary for the purpose of nutrition, 

 although it may possibly occur, but in the Rhodophycecz, because of 

 their aquatic habit, the sporogenous filaments must fuse with the brood 

 cells in order to obtain nourishment from them in the most effective way. 



This view of phylogenetic relationship is made more probable by 

 the researches of Thaxter on the Laboulbeniacece, in which certain 

 representatives are shown to be transitional between the Floridecz and 

 the Ascomycetes. It is certain that the Ascomycetes resemble the red 

 algae more than they do the lower fungi, yet, as we may conclude with 

 Harper, " whether these resemblances are the result of blood relation- 

 ship or merely due to that similarity in the chemical constitution of 

 the protoplasm of different organisms, which under similar conditions 

 enables it to develop structures nearly related in appearance out of 

 rudiments which may be extremely diverse, is likely to remain a 

 puzzling question." 



COLLEMA. 



The much discredited doctrine of Stahl ('77) and others concerning 

 sexuality in certain lichens has received fresh confirmation recently by 

 the researches of Baur ('98) and Darbyshire ('99). Although neither 

 cell nor nuclear fusion has been established beyond all doubt, yet the 

 morphological value of the sexual organs can not be very well ques- 

 tioned. 



According to Stahl, as is well known, the sexual organs of Collema 

 microphyllum occur in large numbers especially upon the illuminated 

 edges of the rapidly growing vegetative lobes of the thallus. The 

 carpogonium arises some little distance beneath the upper surface of 

 the thallus as an ordinary hyphal branch. The lower part, the asco- 

 gonium, consists of a row of short cells coiled up somewhat in the 

 form of a corkscrew, which are distinguished from the other hyphal 

 cells by their larger diameter and denser plasmic contents (Fig. 50, A). 

 The number of cells composing the ascogonium, which makes two or 

 three turns, varies considerably, but may often reach twelve. The 

 ascogonium is continued into a straight filament, the trichogyne, which 

 extends to the upper surface of the thallus. The cells of the tricho- 



