OF ARTS AND SCIENCES. 33 



PANNARIEI. 



In this family, presenting as it does, so many structural character- 

 istics which are emphasized in the true gelatinous lichens, we might 

 fairly expect to find traces at least of the type of sexual reproduction 

 presumably characteristic of the Collemaceous lichens. 



Heppia, Niig. 



The first member of this great family which I have studied accu- 

 rately is the genus Heppia, represented in North America by two 

 species, H. Despreauxii, (Mont.) Tuck. \^H. urceolata, (Njig.) Hepp, 

 H. adrfhitinata, (Krmph.) Mass.], and H. pohjspora, Tuck. The former 

 presents many characteristics which adaj^t it peculiarly to anatomical 

 study. In thin sections of the small thallus lobes we are at once 

 struck by the fact that the fungus hyphte, instead of pursuing a general 

 direction parallel to the substratum, and forming a more or less closely 

 interwoven tissue, occupy a position perpendicular to the substratum. 

 This peculiarity is accentuated, and doubtless induced, by the position 

 of the gonidial algaj. Instead of being scattered singly or in groups, 

 they present a more or less pronounced linear arrangement parallel 

 with the hyphoe. The hyphoe themselves are extraordinarily large, 

 measuring near the substratum 4 ;x in diameter, and increasing rap- 

 idly in size until at the upper surface the individual cells measure 

 18.8 jx X 11.3 /x. The cell walls are very thin, and the hyph;e lie 

 closely packed together, so that the hyphal character of the thallus is lost 

 except near the substratum, where the separate hypliai are smaller and 

 the texture looser. Tlie cortex, when present at all, shows a marked 

 change from that seen in the preceding forms, being reduced on the 

 lower surface to a single layer of rather large thick- walled cells of a 

 brownish color, while the upper surface is destitute of a cortex, unless 

 we accept as our idea of a true cortex Schwendener's statement,* that 

 " only a few layers of cells (sometimes only one) are destitute of go- 

 nidia, and may therefore be regarded as a cortex." The superficial 

 cells, it is true, are covered by a delicate, hyaline, structureless layer, 

 and the superficial cell wall is slightly thickened and colored brownisli, 

 but the differentiation of the cells composing this layer from the cells 

 below is hardly sufficient to warrant our regarding the former as a 

 true cortex. The gonidial and medullary layers are as little to "be 

 distinguished as distinct zones, inasmuch as the algje occupy nearly 



* Schwendener, loc. cit., p. 178. 



VOL. XXV. (S. S. XVII.) o 



