34 PROCEEDINGS OF THE AMERICAN ACADEMY 



the full depth of the thallus ; in fact, the whole character of the thal- 

 lus would lead us to regard Heppia as one of the terminal members 

 of a transitional series of forms connecting the heteromeric and homce- 

 omeric groups.* 



I have before referred to certain peculiarities exhibited by the algas 

 of this lichen. Their peculiar arrangement, brought out most plainly 

 with the low power, seems to indicate that we have to do with an 

 originally filamentous alga, the elements of which have become par- 

 tially disjilaced and altered in form by the encroaching hyphee. This 

 view is confirmed when, on crushing a section of the thallus, we are 

 able to separate short chains consisting of four or five large, bluish- 

 green cells. The analogy between these chains or filaments and the 

 filamentous alga Scytonema, Ag., was first pointed out by Bornet,t and 

 an examination of the species before us leaves no doubt of the truth 

 of the analogy, although I have not as yet found the filaments still 

 invested by the gelatinous sheath characteristic of Scytonema. Such 

 filaments, however, do occur in all cases, upon the substratum under 

 and around the thallus-lobes. 



The origin and development of both spermogonia and apothecia 

 differ only in minor particulars from what has already been observed 

 and described in other lichens. The former are extremely small, a 

 fact which, taken in connection with their rather infrequent occur- 

 rence and inconspicuous character, might cause them to be overlooked. 

 Careful sections, however, near the edges of the thallus-lobes bring to 

 light, generally just below the median line of the section, small hyaline 

 areas in the midst of the surrounding algve which on further examina- 

 tion are resolved into ovoid masses of delicate interwoven hyphae. 

 The later stages of development may be readily followed, and, being 

 similar to those already described, are too familiar to need repetition 

 here. By the time the apex of the young spermogonium has reached 

 the surfiice, the central portion of the mass has been absorbed, and a 

 pore is formed by a schizogenetic process, the hyphas forming the short 

 neck separating in the centre and forcing apart the parallel hyphae 

 surrounding them. The primordia of the apothecia resemble very 

 closely the young spermogonia, except in size. When still distinguish- 

 able in the thalline tissue as only a dense, spherical mass of delicate, 

 hyphal bi-anches, they are already more than twice the size of the 

 spermogonia of the corresponding stage of development. At this early 



* Cf. Koerber, Parerga Lich., p. 2G. 



t Bornet, Ann. des Sci. Nat., Scr. V., Vol. XVII. 



