﻿304 Evans: The genus Plagiochasma 



Although the appendages are much like those of P. Landii and 

 P. Wrightii they are distinguished from the first by their blunter 

 apices and from the second, usually at least, by their narrower 

 form and lack of basal constrictions. 



In proposing Aitonia japonica as a new species Stephani 

 emphasized the solid elaters and spoke of them as a unique 

 feature, apparently overlooking the fact that Gottsche had as- 

 signed similar elaters to P. intermedium many years earlier. In his 

 Species Hepaticarum, however, Stephani recognizes both P. 

 japonicum and P. intermedium and ascribes solid elaters to both. 

 A comparison of his descriptions brings out the following dif- 

 ferences. In P. japonicum the thallus is said to be dichotomous 

 and to innovate from the apex and laterally from the midrib ; the 

 epidermal cells to have trigones, and the pores to be surrounded 

 by three or four concentric series of cells with six to eight cells 

 in each series; the appendages of the ventral scales to be ovate- 

 oblong or elliptical; the carpocephalum to be plano-convex with 

 rounded lobes; and the spores to be 50^1 in diameter. In P. 

 intermedium the thallus is said to be rarely dichotomous but to 

 innovate from the apex; the epidermal cells to have thick walls 

 but no trigones; the pores to be surrounded by three concentric 

 series with eight cells in each series; the appendages of the ventral 

 scales to be strongly constricted, ovate-oblong, acute, and entire; 

 the carpocephalum to be concave, the lobes showing erect- 

 recurved and connivent horns; and the spores to be 60 m in di- 



It will at once be seen that most of these differences are slight 

 or relate to characters which may be expected to be variable. 

 Those drawn from the epidermal cells and from the carpocephala 

 seem at first sight to be more important. Unfortunately they prove 

 to be either inconstant or based on hasty observations. The 

 epidermal cells in P. intermedium, for example, have distinct 

 trigones even if they are sometimes small; and the carpocephala 

 in Yoshinaga's specimens of P. japonicum are distinctly concave 

 at the apex and show apiculate lobes, agreeing with the usual 

 condition in P. intermedium. The writer, in fact, has been able 

 to find no valid characters distinguishing the North American 

 from the Asiatic species and therefore feels compelled to reduce 

 the latter to synonymy, in spite of its wide geographical separation. 



