122 Knud Jessen. 



found with green leaves during winter. Pot. maculata is 

 however an exception, as it must undoubtedly be called 

 a true evergreen; but in comparison with the other herba- 

 ceous Potentillas its leaf-structure does not exhibit any 

 special xeromorphic characters. 



Among the 14 species of Arctic Ranunculaceæ, which 

 I have investigated 1 , there are only two, at most three 

 species, the leaves of which have a xeromorphic character, 

 viz. Thalictrum alpinum and Coptis trifolia which have 

 leathery leaves, which in the latter live at least two years, 

 and Ran. glacialis with a somewhat succulent leaf which 

 has a well-developed palisade-tissue. Of the remain- 

 ing species all the land-plants have a decidedly meso- 

 morphic leaf-structure. By comparison of the individual 

 leaf-tissues in the species of Ranunculaceæ and Rosaceæ 

 which have been investigated the difference between the 

 two families is distinctly seen. 



The epidermis in all the Ranunculaceæ, with the excep- 

 tion of certain forms oiRan. acer., is glabrous or only slightly 

 hairy. The outer wall of the epidermis of the upper leaf- 

 surface, except in Thalictrum alpinum and ('optis trifolia, is 

 thin, not above 2p thick, and the walls are not mucilaginous 

 as in the Rosaceæ. In the paper cited it is recorded that 

 chlorophyll was usually found in the epidermis of the leaf 

 of the Arctic Ranunculaceæ which had been investigated, 

 but I did not observe this in the Rosaceæ which I have 

 had for investigation. The stomata in our Ranunculaceæ 

 are always situated on a level with both leaf-surfaces, 

 and as in the Rosaceæ, they occur especially upon the 

 lower surface of the leaf; three of the species have, how- 

 ever, the majority of their stomata upon the upper 



1 The Structure and Biology of Arctic Flowering Plants, I. 6. 

 Ranunculaceae by Knud Jessen. Medd. om Grönland, XXXVI, 

 Kobenhavn, 1911. 



