American Species of Marchantia. 311 



that this was hardly possible. Many instances were noted where 

 the range of one type overlapped that of another, and a few 

 cases were observed in which appendages of two distinct types 

 occurred on -an individual, thallus (Figs. 15, H, I; 17, A, B). 

 It was impossible, moreover, to associate the differences in the 

 appendages with other differences showing any degree of con- 

 stancy. In the writer's opinion, therefore, the numerous types of 

 appendage are to be regarded as a further evidence of the great 

 variability of the species. 



In the case of the involucres there is again great variability, 

 although the extremes are perhaps less marked than in il/. domin- 

 gCHsis. Fig. 20, L, shows an involucre in which the teeth are 

 scattered, short, and blunt ; while in Fig. 20, J, K, M, the 

 involucres shown bear crowded, long and slender teeth. It will 

 be noted that some of the teeth are simple while others are more 

 or less complex. Bifid teeth are especially common and often 

 show widely divergent divisions. The involucres are firmer than 

 in AT. domhigensis, the cell walls being sometimes distinctly 

 thickened and pigmented with yellowish brown. 



In North America the only species with which M. cJienopoda 

 is likely to be confused is M. domingcnsis. The two species are 

 of about the same size, the structure of the epidermal pores is 

 much the same in both, the sclerotic cells in the ventral portion 

 of the thallus show a similar distribution and the male recep- 

 tacles are very much alike in general appearance. There are, 

 however, striking differences which usually make it possible to 

 distinguish specimens even in the absence of female receptacles. 

 In M. chenopoda slime cells can almost always be observed in 

 the thallus and often occur in great abundance; the appendages 

 of the ventral scales are often entire and are never very closely 

 toothed ; and the stalk of the male receptacle is destitute of air- 

 chambers. In M. domhigensis there are no slime cells in the 

 thallus ; the appendages of the ventral scales are closely toothed ; 

 and the stalk of the male receptacle bears a band of air-chambers. 



If female receptacles are present other important differences 

 may be observed. In M. chenopoda, the stalk bears two bands 

 of air-chambers ; there are normally only five lobes, these being 

 very short; and the involucre is firm in texture, the margin 

 varying from dentate to ciliate or laciniate. In M. domingensis 

 the stalk bears a single band of air-chambers, there are usually 



