OF ARTS AND SCIENCES. 37 



themselves, thus increasing very rapidly the area of the disk. But al- 

 ready this disk is elevated above the surface, and, being free to expand 

 on all sides, spreads out in a fan-like manner, its edges encroaching 

 more and more upon the thalHne surface around it. Finally the hyphfe 

 forming the central area of the disk give rise, from their tips, to elon- 

 gated cells, which may at once grow into either asci or parapliyses, or 

 may again bifurcate and produce the asci and paraphyses as a second 

 order of branches. (Plate II. Figs. 13-16.) 



The tips of the hyphae, which, by the spreading out of the margin of 

 the apothecium over the thallus, have come to be directed obliquely, or 

 even perpendicularly, to the surface, elongate, and though I have been 

 unable to see with certainty any definite anastomosis between these tips 

 and the cells composing the thalline surface, they undoubtedly serve to 

 attach the lower surface of the apothecium to the surface of the thallus. 

 The extremely gelatinous character of the mature apothecium may be 

 seen from the fact that when wet it becomes almost transparent, so that 

 small foreign bodies on the surface of the thallus may be seen with a 

 hand-lens through the tissue of the overspreading apothecium. This 

 gelatinous quality renders it a matter of extreme difficulty to separate, 

 sufficiently for exact study, the elements of the hymenium. With care 

 and patience, however, it may be done. The asci are colored blue with 

 any preparation of iodine, but no other part of the apothecium is so 

 affected, nor at any stage in its growth, as far as my observation goes, 

 does treatment with iodine bring to light any differentiated cells which 

 might be mistaken for ascogonium, trichogyne, or ascogenous cells. 

 The whole process of growth seems to be a purely vegetative one. 



Pannaria rubiginosa, (Thunb.) Delis. 



In the group of Pannaria species represented by P. rubiginosa we 

 have a still nearer approach to the Collemaceous type. The anatom- 

 ical structure of the thallus, while on the one hand, by reason of the 

 presence of a thick cortex investing the upper surface and the absence 

 of cortex on the lower surface, it seems to revert to the Peltigera 

 type, seems on the other hand, from the nature of the alga? and the 

 character impressed upon the thallus as a whole by that nature, to be 

 differentiated widely from all preceding types. The algae occupy 

 nearly the full depth of the thallus, and at first sight present the 

 appearance of irregular groups of small bluish-green cells embedded 

 in spherical masses of jelly. By crushing a thin section, however, the 

 cells composing these groups are seen to be arranged, not in straight 

 filaments as in Heppia and Pannaria molybdea, but in curved chains 



