DESCRIPTION OF THE SPECIES. 193 



It seems to have been split off loii<^!tiulinally from a trunk so as not to 

 show any portion of the terminal bud. It has no axillary buds. The 

 cross-sections of the bases of the petioles resemble those of No. 2, but 

 are somewhat higher proportionally, being 14°"" in height, against only 

 20""" in length. 



We may from the above detailed account sum up the description of 

 the species as follows : 



Ty.sonia Makvl.^ndica, .sp. nov. 



Plates CLXXIV-CLX.XX. 



Stems ovate or oblong, more or less flattened, medulla comparatively 

 small ; woody zone large, external integument, with the bases of the 

 petioles, very thick ; male inflorescence probably borne on a stalk on the 

 summit of the trunk by the side of the bud of growth of the trunk, and 

 carried on a trunk without axillary buds; female inflorescence on axillary 

 growths; growth of the trunk maintained by a terminal bud, which un- 

 folded successive circles of leaves. 



Localities all in Maryland, viz : Spring Garden, at Baltimore ; near 

 Contee's station ; near Beltsville. 



CONIFER^C. 



The conifers form the most important element in the Potomac flora. 

 Taken as a whole they lend a decidedly ancient aspect to this flora A 

 number of the most important of these conifers have passed entirely 

 away, leaving no living species. The genera still surviving and most 

 nearly allied to these more important Potomac forms aj>pear now very 

 locally distributed and contain few species. Indeed we may regard them 

 as in process of extinction. Such of them as have hitherto been found in 

 other parts of the world are here much more abundantly represented. 



The conifers are largely developed in variety of types and in the 

 number of individuals belonging to the different types, as well as in the 

 very general diffusion of the forms. In the number of different species 

 the conifers are inferior to the ferns, but they far surpass the ferns in the 

 number of individuals belonging to each species. They are much more 

 MON XV 13 



