178 THE S ALTON SEA. 



of wax and resinous material on the epidermis, retardation and restriction of the develop- 

 ment of branches and shoots, are among the more striking of these features. Spinosity 

 in general results from the atrophy of branches, but this failure to develop has become so 

 complete in such cacti as the Echinocactus that the entire shoot is cut down to a single 

 cylindrical or globose stem, bearing only spines. 



The halophytes, many of which are cosmopolitan, inhabiting sea-shores in moist 

 climates, comprise both the spinose and succulent types. The latter are represented by 

 Spirostachys and Svxjeda, and the former by Distichlis, Atriplex, and Pluchea. The con- 

 centration of the sap of the halophytes is midway between that of the spinose forms and 

 of the cacti. A distinction is to be made between the cosmopolitan succulent types and 

 those of the salterns and bitterns of the desert. The species from the shore wilt quickly 

 when placed under high evaporative conditions and are therefore much different from 

 the types named above. It is probable that the type as a whole originated in charged soils 

 in arid regions. It does not seem to be going too far to assume also that these conditions 

 are identical with or fairly similar to those now prevalent in the Sal ton Sink and elsewhere. 

 The xerophytes and halophytes of the Salton Sink are therefore to be seen living under the 

 conditions coincident or causal to their evolutionary development. It will not be profitable 

 to venture an analysis of the environmental complex in an effort to detect possible causality. 

 The only hypothesis hitherto put forward in explanation of this matter is to the effect that 

 succulents, particularly the halophytes, owe their qualities to the inductive action of the 

 chlorides generally present in the substratum, both in saline areas and along seashores. 

 The chief argument seems to have been one of coincidence, and no note was taken of the 

 fact that succulent halophytes also belong in the bitterns in which the salts are carbonates 

 and sulphates. 



One condition of the environment is universal in deserts, the high evaporating capacity 

 of the air, the effects of which are to be seen even in many plants with an abundant supply 

 of soil-moisture and whose shoots are exposed to desert wind-action. This state of affairs, 

 conducive to a high rate of water-loss, is generally manifested or accompanied by the 

 restriction of leaves, the induration of surfaces, and the atrophy of shoots exhibited by 

 spinose and succulent xerophytes and halophytes. A general parallel is offered by the 

 behavior of a dish of hydrated gelatine which may be exposed to the air under high evapora- 

 tive conditions. If the conditions of desiccation were of the intensity of the desert, the 

 outer surface would soon become coagulated and the hardened surface would thus effectu- 

 ally check the loss of water from the layers beneath. This in its final analysis is what 

 takes place in the body of the plant. The expanding shoot is a structure of plasmatic 

 colloids and the loss of water or other features which would tend to coagulation of expand- 

 ing cells would check their growth and be followed by atrophies of various degrees. The 

 actual form of the shoot of the plants so affected would of course be modified in the most 

 serious manner according to the special morphological features presented, and it is to be 

 imderstood that the stele and the general morphogeny of the type were determined pre- 

 vious to their encounter with the conditions of aridity; yet with the widest diversity of 

 actual surface, shape and size of organs, stomatal variations, and seasonal habit, results may 

 be seen suggestive of the hardening or coagulatory effects of high evaporatory rates, and the 

 coincidences are so sweeping and universal as to suggest that a causal connection is present. 



If it be assiuned that the modification of the extent of development of the shoot may 

 be connected with physical agencies directly external to this member and acting directly 

 upon it, there remains the question of succulence to be accounted for. 



Succulence in general entails the exaggeration of parenchymatous tissue, cortical or 

 medullary, and the accumulation in the resulting enlarged tracts of a surplus or balance 

 of water, which physiologically forms a pocket or reservoir with respect to the transpira- 

 tion stream. Such tracts may be developed in roots, stems, or branches — or even in leaves, 



