OF ARTS AND SCIENCES. 21 



the Ascomycetes. It seems iiertinent, therefore, to ask why we should 

 expect to find throughout the lichens this highly differentiated form of 

 reproduction alone. Should we not rather, arguing from analogy, ex- 

 pect to find many modifications of this type, starting with that seen in 

 the Collemaceae which connects that group more or less definitely with 

 the Floride^, and including in the series some, if not all, of the modi- 

 fications existing in such ascomycetous fungi as Polystigma, iu which 

 a trichogyne, while present iu the form of a prolongation of a coiled 

 ascogonium, takes no share in the formation of asci, — Pyrouema, in 

 which fertilization is effected between the swollen tips of adjacent hy- 

 phal branches by means of a tube put out from one of the tips (the 

 male cell or antheridium) which fuses with the tip of the female cell 

 or ascogonium, — Podosphasra, Erysiphe, Eurotium, and Ascobolus, 

 where a coiled ascogonium is fertilized directly without the interven- 

 tion of a trichogyne, by jjrotoplasmic union between its tip and that of 

 a specialized branch arising in its neighborhood, — and, finally, the 

 sclerotia-forming Pezizae and the Morchellse, in which, with the dis- 

 appearance of the carpogonium, the last traces of sexual organs are lost 

 entirely and reproduction becomes purely a vegetative process ? 



The present paper embodies the results which I have obtained from 

 the careful examination of certain species of lichens presumably most 

 nearly related to the Collemacete, with the twofold object of either 

 proving or disproving, in the lichens examined, the existence at any 

 time of two separate systems of hyphas in the fruit, and the occur- 

 rence of some form of sexual reproduction, I was led to a discussion 

 of this topic by a paper recently published in " Flora," * which deals 

 with the same questions. The writer, after examining nine repre- 

 sentatives of the genera Anaptychia, Ramalina, Physcia, Parmelia, 

 Xanthoria, Placodium, Lecanora, and Lecidella, states his conclusions 

 as follows : — 



1. In all species examined, the ascus system and the enveloping 

 system are separate and distinct from each other. 



2. In all there is great similarity in the development of the apothe- 

 cium to that in the Collemaceaj as observed by Stahl. 



The first proposition rests on the presumed fact that there exists an 

 ascogonium from which arise asci only, but Lindau presents no direct 

 proof of this. The second proposition, even if we accept all Lindau's 

 statements, states too much, since there often exists a marked dis- 

 crepancy between his results and those recorded by Stahl. One point 



* Lindau, " Ueber die Anlage und Entwicklung einiger Flechtenapothecien," 

 Flora, 1888, p. 451. 



