100 CAENEGIE INSTITUTION OF WASHINGTON. 



increase of the cells, results in succulence. Not all plants in which 

 such transformations take place become succulents, but two species 

 have been observed in which individuals growing under arid conditions 

 become succulent and those elsewhere maintain their mesophytic 

 character. One, Castilleja latifolia, was found by H. M. Richards to be 

 characterized by a high acidity of the sap in the thin leaves and a 

 lower acidity in the succulent individuals. It is suggested that plants 

 which have a type of respiration resulting in a large proportion of 

 residual acids may be capable of succulency, but this is a matter which 

 has not yet been substantiated by any facts beyond those cited. 



The depletion of the water-supply may, under circumstances as 

 noted above, result in the conversion of polysaccharids into pentosans 

 which take up and hold in a mucilage large proportions of water. This 

 of course is but one of the possibihties. Under other conditions a low 

 water-content causes the formation of the anhydrides, of which wall- 

 substance or cellulose is an example, or, more properly speaking, such 

 action is increased or accelerated, and the plant structure thus becomes 

 hard and indurated, and such use of its carbohydrates is of course 

 accompanied by a limited growth, particularly in branches and leaves 

 where the effects of aridity would be greatest. 



The separate types of transformation of carbohydrates might take 

 place in the same plant, in different cells. Thus, some of the massive 

 cacti have shoots from which the power of branching has been entirely 

 lost and the stems are reduced to short, cylindrical, swollen, or globose 

 forms. The external layers of such plants exhibit the typical xero- 

 phytic anhydrous wall-formations, while the cortical elements have 

 been the scene of transformations of sugars resulting in succulency. 



The exposure of a plant to arid conditions might be expected, there- 

 fore, to be followed by a retarded development due to the lack of water 

 necessary for the hydration of cell-colloids in growth, by the accelerated 

 formation of pentosans or mucilaginous material in the cells, leading 

 to hypertrophy of the parenchymatous elements, or by the increased 

 formation of wall material, especially in the external layers constituting 

 the essential feature of xerophytism. 



The conclusions reached in this and in previous papers are to the 

 effect that succulence results from the conversion of polysaccharids 

 into pentosans or mucilages, and xerophytism from a conversion of the 

 polysaccharids into the anhydrides or wall material, both transforma- 

 tions being induced by a depleted or lessened water-supply in the cells. 



Transpiration and Absorption by Roots of Fleshy Euphorbias, by Edith B. Shreve. 



The transpirational and root-absorption behavior of 3 species of 

 fleshy euphorbias has been studied to ascertain whether or not they 

 have any physiological resemblance to the species of cacti which have 

 been previously investigated. The methods used have been described 



