114 AERATION AND AIR-CONTENT. 



less do not avoid the windiest and most unfavorable habitats. The 

 most notable are Rubus chamcemorus, Pedicularis lapponica, Nar- 

 dosmia frigida, Ranunculus pallasii, and, even more sensitive, Hip- 

 puris, Caltha, Epilobium palustre and davuricum, Cardamine pratensis, 

 Comarum, etc. Their specific property seems to be a raising of the 

 functional ability of the tissue to a maximum of resistance against 

 cold. 



Schimper (1890) stated that devices which indicate inadequate 

 water relations occur among plants of many habitats, where they 

 can be explained neither through low water-content nor inheritance. 

 His researches showed that in all cases where protective devices 

 against transpiration were found in the structure of plants a need for 

 such protection actually existed, but that this might be brought about 

 by very different causes. For example, such protective devices are 

 quite common in the case of halophytes, alpine plants, and ever- 

 green woody plants of the north temperate zone. Protection against 

 transpiration is necessary for halophytes on account of the greater 

 difficulty of absorption resulting from the high salt-content, and be- 

 cause concentrated solutions of salt hinder photosynthesis, while 

 still more concentrated ones result in the death of the organs. The 

 alpine flora of Java owes its highly peculiar impress not to low tem- 

 peratures, but to protective devices against transpiration. It is 

 clear that the rarefication of the air, together with its direct influence 

 upon transpiration and the indirect influence of the stronger inso- 

 lation, is to be regarded as the most important cause of timberline 

 and of the xerophyll character of these tropic alpine formations. The 

 flora of the solfataras has a pronounced xerophytic character, and 

 there can be no doubt that here, as in the case of the mangrove, the 

 chemical nature of the substratum makes protective devices against 

 transpiration a necessary condition of life. The retarding effect of 

 a lower temperature of the soil upon the water absorption of the 

 plant makes it also conceivable why alpine plants that grow in melted 

 snow, like Ranunculus glacialis, or on glacial streams, like Saxifraga 

 aizoides, exposed to the glowing rays of the alpine sun, are thick- 

 leaved or succulent, like the inhabitants of dry habitats. Moreover, 

 the peculiarities of polar plants, which show so many analogies with 

 those of deserts, may be related to similar causes. Biologically all 

 these peculiarities are wholly intelligible, and it is only necessary to 

 advance proof that such protective devices occur in all plants which 

 permanently or periodically have to contend against a lack of water, 

 whether the cause is to be sought in dryness of the air and soil, in 

 stronger insolation and rarefication of the air, in the salt-content of 

 the soil, or in the lower temperature of the latter. 



Goebel (1891 : 11) investigated the discrepancy between habitat 

 and adaptation in the vegetation of the Paramos of Venezuela. The 

 greater humidity was regarded as causing the greater luxuriance in 



