20 PROCEEDINGS OF THE AMERICAN ACADEMY 



in both trichogyne and ascogonium point to the probability of sucK a 

 union. In the trichogyne these changes are seen in the progressive 

 thickening of the septa from the tip inwards, while the cells of the as- 

 cogonium begin to multiply in number. The vegetative hyphse in the 

 neighborhood then proceed to branch profusely, enveloping the asco- 

 gonic cells, and finally putting out among and between the latter a 

 series of parallel threads, ai'ising perpendicular to the surface, and 

 forming the first paraphyses. The asci arise solely as ultimate 

 branches of the ascogonic cells, and thus the two systems forming the 

 young hymenium are from the beginning quite separate and distinct 

 from each other. 



These facts have been observed in detail only in the Collemacese, 

 and Stahl explains them on the ground that the coiled ascogonium is 

 analogous to that seen in Eurotiura and Sordaria both in form and in 

 later development, the absence of the trichogyne in these forms being 

 due to the suppression of motile male bodies and the introduction of 

 fertilization by a process' of fusion between neighboring specialized 

 branches. He considers the trichogyne as quite analogous to the 

 organ of the same name in the Florideae, and from these considerations 

 he draws the general conclusion that all lichens are probaby provided 

 with a form of sexual reproduction analogous in some respects to the 

 Florideae, and in other respects to certain ascomycetous fungi. But 

 such a generalization is at least premature when we consider that it 

 is only in the peculiar group of the Collemacese that these analogies 

 have been traced. 



With this question concerning the sexuality of lichens there has 

 recently been connected another of almost equal importance. In all 

 ascomycetous fungi in which some type of sexual reproduction has 

 been certainly observed there are also found to exist two separate 

 systems of hyphte in the fruit, — the ascogenous system, arising 

 from the ascogonium, and consisting of asci only, and the envelop- 

 ing system, arising from the hyphae surrounding the ascogonium, and 

 consisting of the paraphyses and the tissue enveloping the hyme- 

 nium. This fact is so marked a feature of sexual reproduction in 

 fungi, that it seems fair to conclude that it is characteristic of such re- 

 production. Both these points are brought out prominently by Stahl 

 in his investigations on the Collemacea?, but here agam the generali- 

 zations made by Stahl, and almost tacitly accepted by many later ob- 

 servers, are certainly not to be accounted for on grounds of analogy. 

 The lichens, exclusive of the hymenomycetous and gasteromycetous 

 forms, are now considered generally to belong to the great class of 



