438 



leaves of these two species have no stomata and few stomata 

 respectively; in the bifacial leaves they are more numerous 

 upon the upper surface. 



B. The aerial leaves. All the species of Ranunculus 

 with the exception of R. reptans and R. glacialis may, with 

 regard to the structure of their leaves, be referred to the same 

 sub-group. The leaves are glabrous or slightly hairy (except 

 in R. acer), the epidermis is thin-walled and the palisade-tissue 

 and spongy parenchyma are homogeneously developed in all 

 the species ; from one to two palisade-layers occur which con- 

 stitute about one-half of the thickness of the mesophyll, and 

 the. individual palisade-cells are often barrel-shaped and some- 

 what irregular; the spongy tissue contains numerous inter- 

 cellular spaces and the cells are branched in a stellate manner. 

 In R. hyperboreus the stomata were more numerous upon the 

 upper surface, and in R. Pallasii their number was equal upon 

 both surfaces, but in the other species they were more nu- 

 merous upon the lower surface. The habitat of all is usually 

 damp moss. 



R. glacialis differs from the above-mentioned species in 

 its better developed palisade-tissue and in the looser structure 

 of its spongy parenchyma. The stomata are most numerous 

 upon the upper surface. It grows in localities which are poorer 

 in humus than those in which the other species of Ranun- 

 culus grow. 



In Greenland Anemone Richardsoni is doubtless especially 

 a shade-plant; in the structure of its leaf it closely resembles 

 Anemone nemorosa. Stomata occur almost exclusively upon 

 the lower surface of the leaf. 



Of the species which have been examined Thalictrum alp. 

 and Coptis trifolia are the most xerophytic. The leaves are coria- 

 ceous and the epidermis is thick, especially in Thalictrum alp. 

 The palisade-cells occur in 2—3 compact layers; the spongy 

 parenchyma consists of shortly branched cells. In both species 



