Rosaceæ. 123 



surface of the leaf, viz. Ran. glacialis, R. hyperboreus and 

 R. reptans. The pahsade-tissue is on an average some- 

 what more strongly developed in the Rosaceæ than in 

 the Raniinculaceæ, and the intercellular spaces are usually 

 smaller. It is recorded that the palisade-tissue in the 

 Ranunculaceæ constitutes about one-half of the thickness 

 of the mesophyll, but in several of the species it is, how- 

 ever, considerably less thick, e. g. Anemone Richardsoni, 

 Ran. Pallasii. Ran. pygniæus and Ran. nivalis. The respi- 

 ratory tissue is on an average looser in structure in the 

 Ranunculaceæ. Several of the Ranunculi have leaves 

 which in their anatomical structure recall the type which 

 is common among woodland plants in temperate regions, 

 thus especially R. pygmæus and R. nivalis, and a similar 

 structure is found in Rubus arcticus and Rub. saxatilis. 



The fact that the leaves of the Ranunculaceæ which 

 have been investigated, are, as already mentioned, on 

 the whole, to a greater extent mesomorphic than are 

 those of the Arctic Rosaceæ is I find, partially explained 

 — as in the Rosaceæ — by a consideration of the habitats. 

 It is commonly stated that the Arctic Ranunculaceæ 

 prefer damp localities, often bogs; thus Ranunculus 

 reptans, Ran. hyperboreus, Ran. lapponicus. Ran. Pallasii 

 and also Ran. af finis, Ran. nivalis. Ran. pygmæus. Ran. 

 sulphureus and Ran. glacialis are mountain plants that 

 live near the snow line in soil saturated with melting snow. 

 Anemone Richardsoni lives by preference in copses, and 

 Thalictrum alpinum and Coptis trijolia are met with in 

 similar localities, or at any rate on luxuriant heaths. 

 Ran. acer, on the other hand, often occurs on rather dry 

 and stony soil, and in such localities its leaves are 

 more hairy. We have, however, a peculiar instance of 

 the fact that different plants react differently under appa- 

 rently the same conditions. Thus, both Potentilla palu- 



