1903] Yukon Hepatic^. ly 



Hunker Creek [s^i, 57); Dawson (Williams), not listed 

 by Howe. New to America. Previously recorded from Siberia 

 only. The Yukon material has been compared with Siberian 

 specimens kindly communicated by Dr. Arnell. 



The genus Mesoptychia is allied to Lophozia and also to 

 Acrobolbus, both of which have succubous, alternate and 

 variously lobate leaves. It is distinguished from the first ot 

 these genera by the possession of a perigynium and from the 

 second by the possession of a perianth. The perigynium ot 

 Mesoptychia is further distinguished from that of Acrobolbus 

 by being hollow and by carrying down with it, as it develops, 

 the unfertilized archegonia. The occurrence of both perianth 

 and saccate perigynium in the same plant is a most remarkable 

 feature but is not entirely unique, for we find it duplicated in 

 Arnellia. In this genus, however, the leaves although 

 succubous are undivided and opposite, coalescing in pairs at 

 their antical bases, and the underleaves are simple. In the 

 genus Gyrothyr'a as well as in Nardia hcBmatosticta and the 

 allied A^. Breidleri, we also find a certain approach to the 

 condition described for Mesoptychia. In these plants the end 

 of the female branch becomes fleshy after fertilization and 

 forms an erect perigynium, which encloses the developing 

 sporophyte. On the outside of this fleshy perigynium are 

 borne the perichastial bracts and at its mouth the rudimentary 

 perianth. The lower part of the perigj'nium extends down- 

 ward as a small solid bulbous enlargement, into which the 

 foot of the sporophyte penetrate more or less deeply. In 

 Gyrothyra the unfertilized archegonia remain near the mouth 

 of the perigynium, somewhat as in Acrobolbtis, while in the 

 two species oi Nardia they are found at the bottom. The most 

 essential difference between the three plants just discussed 

 and Mesoptychia lies in the fact that their perigynia are erect, 

 growing upward at right angles to the fruiting axis, while in 

 Mesoptychia they are pendent and grow downward. There 

 are of course many other diff'erences drawn from purely vege- 

 tative characters. 



As in other saccate genera, the development of the peri- 

 gynium in Mesoptychia is dependent upon fertilization. The 



