122 KEARNEY: PLANT LIFE ON SALINE SOILS 



epidermal glands, the cells of which are very rich in proto- 

 plasm and have a large nucleus. The process of excretion by 

 these organs is not a passive filtration, but a true glandular 

 activity, as has been demonstrated by the writer^'' and by 

 Ruhland.^^ The latter investigator also obtained fairiy conclu- 

 sive evidence that the salt content of the leaves is materially 

 reduced when excretion is actively taking place. 



It would seem to be significant that as a rule the species which 

 excrete salt do not possess a highly developed water-storage 

 tissue. On the other hand, salt excretion is not known to occur 

 in the Chenopodiaceae, the largest and most important of halo- 

 phytic families. This family includes numerous genera in which 

 water-storage tissue is exceptionally well developed. 



PHYSIOLOGICAL CHARACTERISTICS OF SALT PLANTS * 



From what has been said, it is evident that there are man}" 

 gaps and many apparent contradictions in our knowledge of the 

 normal physiology of the salt plants. Two characteristics, 

 however, are general and may be said to be conditioned by the 

 nature of the environment. These are 



1. Ability to develop a high osmotic pressure in the cells of 

 the absorbing organs, thus allowing water to be taken up from 

 solutions of a concentration which would inhibit absorption in 

 nonhalophytic species. Coupled with this, is the power of ac- 

 commodating the pressure to (often rapid) changes of concen- 

 tration in the medium. 



2. Ability to carry on normally all essential physiological 

 functions, notwithstanding the presence of salt in the cell sap in 

 quantities which, in nonhalophytic species, would seriously ham- 

 per or entirely prevent photosynthesis, metabolism, and growth. 



IMPORTANCE OF SODIUM TO HALOPHYTES 



The problem of whether halophytes can grow in the absence 

 of an appreciable quantity of sodium salts has been the subject 



^^ T. H. Kearney. On the excretion of hygroscopic salts in Frankenia and 

 Statice. Science N. S. 19:419. 1904. 



*^ W. Rtthlaxd. Die Salzdriiscn dcr Plumbag i naceen. Jahrb. Wiss. Bot. 

 55:409. 1915. 



