130 BOOKS AND CURRENT LITERATURE 



carried above 14,500 feet into the region of nightly occurrence of frost. 

 Arborescent cacti are abundant up to elevations of 11,500 feet, and 

 isolated patches of quenigo woodland are found in the cloud belt at 

 14,000 feet. 



It is impossible to give in this place the extended notice which is 

 due the physiographic work accomplished by Bowman. In addition 

 to this material, however, his book is replete with observations of in- 

 terest to every student of the relation of organisms to environment. — 

 Forrest Shreve. 



Tolerance of Fresh Water by Marine ■ Plants. — In a recent 

 paper^ Osterhout points out that tolerance of fresh water by marine 

 plants is not strictly due to gradual adaptation, as has been supposed. 

 In the case of eel grass (Zostera marina), with which the author experi- 

 mented at Mount Desert Island, Maine, the same differences oc- 

 curred in the leaves and roots of plants growing in the mouths of streams 

 and plants growing in salt water remote from the mouths of streams, 

 in their abihty to withstand fresh water. Eel grass growing in the 

 ocean near the mouths of streams has the leaves immersed in a layer 

 of water that is alternately fresh and salt, and its roots embedded in 

 mud which is almost constantly uniformly saline, while the same 

 species growing away from estuaries has both leaves and roots immersed 

 in a salt medium. Leaf cells in both cases withstand exposure to fresh 

 water for several hom^s, but root cells are quickly killed. That the 

 longer life of the leaf cells is not due to any difference in cell wall struc- 

 ture is shown by the fact that both leaves and roots were plasmolyzed 

 with equal rapidity when immersed in hypertonic sea water, and then 

 recovered at the same rate when again placed in ordinary sea water. 

 Neither does difference in permeability to water explain difference in 

 behavior, for death is not primarily due to increased water absorption. 

 Following Loeb's point of view, the author suggests that the differ- 

 ence in tolerance of fresh water exhibited by marine plants is due to the 

 difference in outward diffusion from the protoplasm of substances, 

 especially inorganic salts, which are necessary to the normal activity 

 of. their protoplasm. Thus the more tolerant plants lose salts less 

 rapidly than those less tolerant of fresh water. He also suggests as 

 the explanation of this effect, that in the protoplasm of less tolerant 

 plants larger amounts of globulins or other colloids may be present 



. 1 Osterhout, W. J. V., Tolerance of Fresh Water by Marine Plants and its 

 Relation to Adaptation. Bot. Gaz. 63: 146-149, 1917. 



