36 TlMEHRI. 
dorsal on the axis and appressed thereto. Fronds generally pinnately 
divided, rarely simple, often decompound. More or less copiously 
leafy throughout. Prostrate, sub*ere6t, erecT: or scandent. 
Selaginellas differ from their allies the club-mosses by 
possessing two kinds of sporangia and spores, the gene- 
rally distichous arrangement of the leaves, which gives 
the stems a flattened appearance, their more or less 
prostrate or subscandent habit of growth, their uniformly 
communal association and, as a rule, terrestrial location. 
Three or four Lycopodia have a somewhat similar ar- 
rangement of their leaves, and a considerable number 
are terrestrial, and some too are communal, but among 
the Selaginellas these are nearly constant characteristics. 
In a few species, none of which are natives of this 
country, the leaves are all of one kind and multifarious, 
the stems being consequently convolute, as is the rule 
in the Lycopodia. In nearly all the species there is 
some variation of shape in the fronds, and in many 
this is considerable. Some by their habit of rooting 
along the rachis as the growth extends grow to an in- 
definite length and many species are more or less 
modified in size and outline by this habit. In some 
the leaves are the same distance apart on all the 
branches, but in the majority they are widest on the 
primary stem or rachis, being gradually closer on the 
outer ramifications. The ciliation or serration of the 
leaves is generally quite microscopical. They are mois- 
ture and shade-loving plants, and grow principally in 
forests on damp soils or moist ground, forming patches 
or dense carpets or banks of exquisite and, in the differ- 
ent species, variable shades of green ; though a few 
species prefer some degree of exposure. In Europe and 
