1917] Evans, — Notes on New England Hepaticae, XIV 2G5 



In the absence of fresh material the writer has been unable to make 

 a satisfactory study of the present species, but the published descrip- 

 tions and figures bring out most of its essential characters clearly. 

 Aside from the works of Heeg, Massalongo, and K. Miiller, already 

 alluded to, reference may be made to Underwood's account in the 

 6th edition of Gray's Manual, to Howe's critical observations in 

 connection with the Hepaticae of California,^ and to Miss Black's 

 comprehensive morphological study .^ Howe emphasizes the features 

 of the spores, which distinguish the species from all known California 

 Ricciae. He describes them as narrowly margined, 45-55 m in maxi- 

 mum diameter, and covered over almost uniformly "by numerous 

 short, delicate, wavy ridges which rarely anastomose." These 

 peculiarities will serve equally well to separate R. Frostii from the 

 other New England species of Riccia, in all of which the ridges on the 

 spores form regular meshworks. 



Whether R. Frostii should be retained in the genus Riccia or trans- 

 ferred to Ricciella is not altogether clear. The green tissue contains 

 intercellular canals which extend, in some cases at least, from the 

 compact ventral tissue to the dorsal surface. Whether they are 

 always continuous for this entire distance, or whether they are occa- 

 sionally subdivided by transverse or oblique partitions is not brought 

 out by the descriptions. In any case the canals are broader than in 

 typical species of Riccia, and instead of being bounded by only four 

 cells in section view are bounded by several to many cells. In these 

 respects they resemble the marginal canals described by Juel ^ in the 

 case of the European R. Bischoffii Hiiben. Since the median canals 

 in this species are of the narrow type, Juel contends that it shows the 

 Riccia structure in the median portion and the Ricciella structure in 

 the wings, thus forming a connecting link between the two groups 

 and making it unnecessary to recognize Ricciella as a genus. In 

 typical species of Ricciella, however, the intercellular spaces are in 

 more than one layer, so that the genus might still be maintained on 

 the basis of this feature. In the case of R. Frostii, unfortunately, 

 this criterion can not at present be applied, and it therefore seems 

 wisest to retain the species in Riccia, even if certain writers have 

 considered it a Ricciella. 



1 Mem. Torrey Club 7: 32. 1899. 



2 The morphology of Riccia Frostii, Aust. Ann. Bot. 27: 511-532. pi. 37, SS. 1913. 



2 Uber den anatomischen Bau von Riccia Bischoffii Hub. Svensk Bot. Tidskr. 4: 160-166. 

 pi. 7 +/. 1-5. 1910. 



