30 EXPERIMENT STATION RECORD. [Vol.40 



was found that in darkness the rate of water loss tends to become constant, 

 that acidity increases in darkness, and that soluble sugars are broken up, 

 although but little change takes place in the insoluble polysaccharids. These 

 polysaccharids do break down in the course of long confinement, this fact to- 

 gether with that of the resistance of Echinocactus to desiccation helping in a 

 large measure to explain the viability of these plants in spite of long starvation. 



Rate and course of growth of succulents, D. T. MacDougal (Carnegie Inst. 

 Washington Tear Book, 16 (1917), pp. 88-85). — By employing auxographs of im- 

 proved pattern, the author collected much information regarding the growth of 

 plants, more particularly certain cacti, including Echinocactus, Opuntia, Car- 

 negiea, and Mesembryanthemum. These data are briefly discussed. 



The carbohydrate economy of cacti, H. A. Spoehr (Carnegie Inst. Washing- 

 ton Tear Book, 16 (1917), pp. 73-79).— A continuation of studies (E. S. R., 39, 

 p. 224) on the carbohydrate metabolism of the cacti, platyopuntias and Opuntia 

 versicolor, has yielded an insight into various phases of this subject which 

 could not be gained from work with thin-leaved plants. The purpose of the 

 work as a whole is primarily to secure facts bearing upon the problems of 

 photosynthesis, in particular at this stage to secure facts leading to a clearer 

 understanding of the conditions governing the equilibria and mutual trans- 

 formations of the groups of carbohydrates in the leaf and of the fate of these 

 substances in the general metabolism. The data obtained are briefly discussed. 



The present report deals with the methods of sugar analysis applicable to 

 plants, seasonal variations in the carbohydrate content of cacti, the effect of 

 temperature and of water content on carbohydrate equilibrium, carbohydrate 

 equilibrium during starvation, and the role of pentose sugars in plant metab- 

 olism. 



Root growth of Prosopis velutina and Opuntia versicolor under conditions 

 of a small oxygen supply in the soil, W. A. Cannon {Carnegie Inst. Washing' 

 ton Tear Book, 16 (1917), pp. 82. 88). — The work here described confirms and 

 extends that previously noted (B. S. R~ 34, p. 334; 3G, p. 525 ; 37. p. 213) as 

 employing carbon dioxid with or without atmospheric air, the present work 

 employing carbon dioxid, commercial oxygen, and commercial nitrogen. 



The rootlets of seedling Prosopis show a variable reaction to small amounts 

 of oxygen, depending apparently in the main on the length of the root. It 

 appears probable that after germination has started root growth may continue 

 for some time under practically anaerobic conditions, the time possibly being 

 related to the duration of the cotyledonary food supply. In 0. versicolor 

 growth in all cases stopped promptly in 2.G7 per cent oxygen. Roots 3 to 7 mm. 

 long stopped growth in 4.56 per cent oxygen, although roots 11 cm. long grew 

 for 48 hours in the same atmosphere. It appears, therefore, that at least the 

 shorter roots of Opuntia cuttings have a greater oxygen requirement than the 

 longer roots of Prosopis seedlings, but that a differential result may also occur 

 which may be associated with the well-known differentia] development of the 

 roots of the species into shallow absorbing and more deeply placed anchoring 

 roots. 



Effect of ammonium sulphate in nutrient solution on the growth of soy 

 beans in sand cultures, M. I. Wolkoff (Soil Set., 5 (1918), A'o. 2, pp. 123-150, 

 figs. 7). — Employing soy beans grown in sand cultures, the author has studied 

 the behavior of ammonium sulphate in the nutrient solution used by Shive 

 (E. S. R., 36, p. 328) as his simplification (E. S. R., 84, p. 333) of that employed 

 by Tottingham. The osmotic concentration of the solutions was in most I 

 below the calculated 2.5 atmospheres. 



