26 EDITH SCHWARTZ CLEMENTS 



3. The adaptation to these factors is the greater the more plastic 

 a species is. 



4. The leaves of alpine plants do not show such thorough pro- 

 tective devices as such great transpiration is accustomed to call 

 forth. The reason for this lies in the greater relative humidity of 

 the air, and greater soil-water. 



5. Since, when exposed to decreased transpiration the alpine 

 plants do not show a reduction but an increase of palisade tissue, it 

 follows that not transpiration but assimilation is more effective as 

 regards the structure of the mesophyll, in such a way that the num- 

 ber and size of the palisade cells are regulated by conditions of as- 

 similation, whereas intercellular spaces are also dependent upon 

 transpiration. 



Lazniewski (96) studied the structure of a number of alpine 

 plants both morphologically and histologically. He classified the 

 plants considered according to morphology, and gave a general dis- 

 cussion of humidities in the alpine regions, noting as of especial 

 importance quick changes and great extremes of both humidities 

 and temperatures. He concluded that one cannot speak of a com- 

 mon alpine leaf type or histological leaf structure, since even among 

 the saxifrages vast differences in the structure of the leaf occur, 

 and wet and dry situations are found close together with the char- 

 acteristic flora. He ascribed the displacement of the palisade cells 

 from a position perpendicular to the leaf surface, to the influence 

 of light. 



Kearney (01) made an ecological study of the distribution of 

 plant species of the Dismal Swamp region. He discussed the most 

 striking adaptations to the habitat as expressed in the histology of 

 the leaf as well as in the morphology of the most abundant or other- 

 wise interesting species. 



Hansgirg (00-03) classified an immense number of leaves into 

 types with respect to external form, and adaptations to climatic 

 conditions. 



Hesselmann (04), in a paper which comes to hand as these pages 

 go to press, has taken up the problem of studying in nature the life 

 processes of plants, and has attempted to gain a conception "of the 

 connection between external factors and plant activities. The in- 

 vestigation, which covers several summers, is thorough and scien- 

 tific. During this period exact records of light, temperature and 

 humidity were made for several stations in the thickets and sunny 



