1917] Evans,— Notes on New England Hepaticae, XIV 265 
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 u 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 3 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. Frostiz, 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. pl. 37, 88. 1913. 
2 Uber den anatomischen Bau von Riccia Bischoffii Hiib. Svensk Bot. Tidskr. 4: 160-166. 
pl.7 +f. 1-5. 1910. 
