GENERAL DISCUSSION. 179 



as in the agaves and crassulas. The plasmatic units or cells are increased in both number 

 and size, growth having been stimulated in both the phases of extension and multiplication. 

 The concentration of the sap in such cells as noted above is generally not very high and 

 in a large number of instances mucilages and gums are present, making the cells practically 

 masses of indefinitely expanding water-absorbing colloids. 



The obvious direction in which to turn, therefore, in the search for agencies which might 

 cause or accompany succulency would be one in which hydratation agencies which would 

 cause the swelling of the colloidal cells would be taken into account. Not until recently 

 would such an inquiry have met with evidence that would be valuable in the discussion 

 of the subject. This evidence is now at hand, however, in the form of the recent writings 

 of Borowikow, as to influence of certain substances upon growth expansions. 1 



The experimentation of Borowikow seems to show that the acids (hydrochloric, 

 sulphuric, nitric, acetic, and boric) witliin certain limits of concentration cause an increased 

 growth of seedlings in a manner corresponding fairly with the swelling of gelatinous colloids 

 treated with the same reagents in equal concentrations. The effect is not due simply to 

 the hydrogen, but is the summed result of both ions. The alkaline metals exert a similar 

 hydrating effect upon gelatine and upon growth. Increase of the concentration beyond 

 certain limits would be followed by coagulatory effects in gelatine and by diminished 

 growth in the plant. Coagulatory effects and retardation of growth are produced by the 

 action of salts of metals, of mercury, copper, strontium, calcium, barium, magnesium, 

 lithium, potassium, and ammonia, which show a diminishing effect upon proteinaceous 

 colloids in the order named. These results suggest a possible means of analysis of the 

 conditions of succulency. The hydratation of the mucilaginous contents of the bodies of 

 certain cacti tested at the Desert Laboratory does not take place in the manner of the 

 growth-effects described by Borowikow, however, and it is evident that the problem is a 

 complicated one. 



The disturbances in the Salton Sink following the making and the gradual desiccation 

 of the lake were of course attended by the exposure of many species to unusual intensities 

 of concentration of some of the substances active in coagulation and in hydratation. But 

 little attention could be given to such environic reactions, yet (as described in a previous 

 section of this paper) noticeable deviations in leaf and stem characters were found in Aster 

 exilis, Prosopis glandulosa, and Atriplex canescens, in addition to variations in the fruits of 

 Scirpus paludosus. The thicker stems and heavier shoots of the first-named species are strik- 

 ingly suggestive of effects such as those ascribed to hydratation action of acids and alkalies. 



The whole possible range of hydratation and coagulatory effects seem to be included 

 in the seasonal changes in the brines described by Professor Peirce in the present volume. 

 Dilute solutions with sodium chloride and calcium salts present seem to be accompanied 

 by hydratation and growth, which are checked with a concentration supposedly increased 

 beyond the optimum. The crystallization out of the sodium and of the calcium and the 

 subjection of the algse to the influence of the magnesium and potassium appear to be fol- 

 lowed by encysting, which may be taken as being due to the neutralizing effect of these 

 substances upon the proteinaceous colloids of the cells. 



The fact that 4 out of a total of 60 species which found place on the strands exhibited 

 modifications of structure not observed elsewhere led directly to a consideration of the 

 endemic species of the Sink. Atriplex saltonensis Parish, Sphceralcea orcutti Vasey and 

 Rose, Cryptanthe costata Brandegee, Calandrina ambigua Howell, Astragalus limatus 

 Sheldon, A. aridus A. Gray, and Chamoesyce saltonensis Millspaugh are to be included 

 in this category. It is true that Calandrina is found a short distance beyond the limits of 

 the Sink, but the remaining 6 species are not known to occur beyond and above the high 



1 Borowikow, G. A. Ueber die Ureachen des Wachstums der Pflanzen, Biochem. Zeitschr., vol. xliv, p. 230. 1913. 



