RED ALG^. 2i9 



young plumules make beautiful microscopical speci- 

 mens, if mounted in some fluid which does not shrink 

 the cells. The beauty, as well as the interest of 

 the specimen, will be enhanced if the plant bears 

 upon the tips of its plumules, the tetrasporic fruit. 

 The color is a darkish purple, more or less red in 

 the younger part^. 



Ptilota densa, Ag. 



This and the two following species belong to 

 California. The frond is compressed, one-eighth of 

 an inch wide, thick, cartilaginous, from three to 

 twelve inches high. The leading stem bears along 

 its edges stout branches, which are either simple or 

 branched, on the same plan as the main stem. The 

 axils of the primary branches make an angle of about 

 45°. The ultimate pinnae, which clothe the edges 

 of the whole plant, are closely set, making a dense 

 border to the frond, of very uniform length, one- 

 tenth of an inch or so, opposite, and very unlike. 

 The one is stout, undivided, incurved, sharply toothed 

 on the outside ; the other opposite, slender, much 

 shorter, pinnately and widely divided. The latter is 

 seen to lie almost hidden out of sight, under the over- 

 arching pinnule which grows next below it. For, 

 it will be observed that, the two forms alternate with 



