﻿284 Evans: The genus Plagiochasma 



lunulate to ovate, while the appendages, one or two In number, 

 are subulate and acute, without constriction at the base (see 

 Fig. 2, A, B). Sometimes, when only one appendage is present 

 there is no sharp boundary where it passes into the basal portion. 

 The deviations from this characteristic condition are shown most 

 clearly in the form of the appendages, which are sometimes ovate 

 and more or less plicate at the base, and in their apices, which 

 may be acuminate or, on the other hand, obtuse or even rounded, 

 several of these variations being sometimes present on a single 

 thallus or in a single clump (Figs. 2, 3). The pigmentation 

 of the scales is usually pronounced, although it may be absent in 

 very moist environments and may disappear to a greater or less 

 extent with age. The cells of the scales are fairly uniform through- 

 out (see Fig. 4, D). Some of the marginal cells occasionally 

 project as blunt or sharp denticulations, and in rare cases a distinct 

 marginal tooth is present. It is much more usual, however, for 

 the margin to be quite entire, and the peculiar slime papillae found 

 in some of the other species are so evanescent that they leave no 

 vestiges. The basal portion of the scale shows scattered cells 

 with oil-bodies, and sometimes one or two such cells are to be 

 seen in the appendages. One of the figures by DeNotaris shows 

 a ventral view of a thallus with several scales in position. One 

 of these scales shows four appendages. The writer has never 

 observed so high a number, although three appendages were found 



In reducing P. italicum to a synonym of P. rupestre Miiller 

 calls attention to the fact that Stephani recognizes both species 

 in his Species Hepaticarum. He adds, however, that he has 

 sought in vain to find differential characters separating them, 

 although he has examined specimens under both names in the 

 Stephani herbarium. He found these to be almost exactly alike 

 even in their details. The differences brought out by Stephani 

 are the following: in P. rupestre, the dioicous inflorescence, the 

 pore surrounded by five cells, the single narrowly lanceolate and 

 acute appendage of the ventral scales: in P. italicum, the monoi- 

 cous inflorescence, the pore surrounded by four cells, the one or 

 two narrowly triangular appendages with broad bases. It will 

 be seen at once that these differences are based on exceedingly 



