22 PROCEEDINGS OP THE AMERICAN ACADEMY 



observed by Stahl, and used by him very. largely as a proof of sexuality, 

 consists in the changes which take place in the trichogyne subsequent 

 to the attachment of one or more spermatia to its tip. This point has 

 not been observed at all by Lindau ; in fact, in one or two cases he fails 

 to observe the trichogyne at all, and merely assumes its existence from 

 analogy. According to Liadau the trichogyne disappears entirely 

 from older primordia in which the ascogonium has become completely 

 enveloped by branches of the neighboring hyphae, whereas Stahl by 

 his figures of Physma compactum, Mass., shows very plainly that the 

 changes in the trichogyne do not take place until the ascogonium is 

 already enveloped by the hyphoe. Furthermore, Lindau confesses that 

 he " is unable to see the briilge-like connection of which Stahl speaks 

 between the spermatia and the trichogyne, although in this case (Ana- 

 pfychia ciliaris) the size of the spermatia might make it easy to see 

 any union if it existed." Stahl bases his distinction between the tri' 

 chogyue and the ordinary vegetative hyphse largely on the fact that the 

 former never branch ; on tiie other hand, Lindau states, in one place, 

 that the primordia may be arrested in their development and then re- 

 vert to the vegetative condition, while in others the young ascogonium 

 bifurcates, and each branch becomes a coiled ascogonium, never revert- 

 ing to the vegetative condition, the latter point being used as a proof 

 that the ascus system is distinct from the enveloping system. There 

 are many other points in the structure of the ascogonium and its share 

 in apothecial formation, which diflfer so widely not ouly from Stahl's ob- 

 servations, but among themselves, that it seems almost incredible that 

 they should occur in groups so nearly related otherwise as those ex- 

 amined by Lindau. We are at least justified in regarding the method 

 of reproduction in the heteromeric lichens as still unsettled, and in 

 continuing careful and systematic investigations upon their structure, 

 until more light is thrown upon it. Taking it for granted that in the 

 groups more nearly related in structure and habit to the Collemacea^ 

 we should find, if anywhere, traces of a form of reproduction found in 

 that group, and a marked separation of the ascus system from the en- 

 veloping system, I began my investigations upon members of the 

 family Peltigerei, genus Sticta. 



The method of investigation followed has been practically the same 

 in all cases. To procure the youngest stages of apothecial develop- 

 ment, I made a large number of sections by hand in the neighborhood 

 of the youngest apothecia visible to the naked eye, and seldom failed 

 to secure the desired stages. This method of making sections I have 

 found preferable to the use of the microtome, inasmuch as the process 



