OF ARTS AND SCIENCES. 31 



margin here equals in thickness the height of tlie paraphyses. They 

 retain more and more their original dimensions as tliey recede from the 

 hymenium, until they are found to present entirely their normal appear- 

 ance as cortical hyphae. Until the apothecium is nearly half the size 

 which it attains at maturity, the asci remain invisihle, being enveloped 

 and covered by the semi-gelatinous membranes of the parajihyses ; but 

 the same treatment which was made use of before serves here also to 

 bring the asci into relief. I have found it advisable, however, in all 

 cases where the membranes of the paraphyses are of so gelatinous a 

 character as in this species, to avoid tiie use of any alcoholic reagent, 

 inasmuch as the alcohol induces a contraction and hardening of the 

 tissue which effectually prevent subsequent maceration. If it is found 

 necessary to stain the asci, an aqueous solution of iodine and potas- 

 sic iodide may be used. Subsequent maceration shows that the sub- 

 hymenial layer consists of branches of the medullary hyphas so densely 

 woven together that a pseudo-parencliymatous tissue results, the cells 

 of which, although in places they still retain a linear arrangement, 

 have as a rule become swollen and distorted by mutual pressure, and 

 are rather larger and more nearly isodiametric than the original hy- 

 phal cells which they represent. From this tissue both asci and para- 

 physes arise indiscriminately, the paraphyses first, and later the asci, 

 pushing up between them. There is no visible differentiation of the 

 subhymenial tissue into ascogenous and paraphyses-beariiig hyphas ; 

 both arise from one and the same tissue of medullary hyph?e, modified, 

 it Is true, but not into two dissimilar systems. (Plate I. Figs. 9-11.) 



Peltigera, (Willd., Hoffm.) Fee. 



Of the genus Peltigera I have examined but one species, P. pohj- 

 dactyla, (Neck.) Hoffm., and very little need be said with regard to it, 

 owing to the similarity existing between it and the other genera pre- 

 viously studied. The thalline structure resembles very closely that 

 of S. amplissima, but approaches more nearly still perhaps that of 

 N. tomentosum, the only important anatomical difference being the ab- 

 sence of the cortex on the lower surface. Peltigera differs carpologi- 

 cally from Nephroma only in the fiict that whereas in the latter, as we 

 have seen, the apothecial primordium arises near the lower algal zone, 

 and when mature occupies the lower surface of the thallus lobe, the 

 primordium in Peltigera arises just below tlie upper algal zone, and, 

 its growth being exclusively toward the upper surface, the mature 

 apothecium occupies that surface. I have been unable in Peltigera, as 

 in Nephroma, to find any trace of a carpogonic apparatus. The origin 



