iQ2o] CURRENT LITERATURE 91 



cannot 



from the early reticulate structures, or that the telophasic alveolization, 

 although irregular, may not later become so equalized as to constitute the 

 first stages of the split; but it does follow that it is quite unsafe to use the 

 principle of telophasic splitting as a premise from which to draw the conclusion 

 that the approximation of thin threads in the early heterotypic prophase 

 represents the reassociation of the halves of a single split chromosome. 

 Although it is well to emphasize the importance of the premeiotic telophase, 

 the ultimate solution of this perplexing problem must be reached mainly 

 through a more refined analysis of those prophasic changes which have led a 

 long list of investigators to the conclusion that the early heterotypic association 

 of threads represents a conjugation of entire chromosomes which separate at 



heterotyp 



figu 



English cytologists do not prove the theory they advocate. — L. W. Shaep. 



Carbohydrate economy of cacti. — A distinct contribution to our knowledge 

 of the carbohydrates in plants in general, and in the succulents in particular, 

 is the report of Spoehr's investigations at the Desert Laboratory. 8 The 

 methods employed give us what is probably the most complete analysis of the 

 carbohydrates of a single plant tissue that we have, values for no less than 

 11 different groups of carbohydrates being ascertained, partly by direct 



determinations and partly by calculation. 



The monograph is prefaced by a rather thorough discussion of carbo- 

 hydrate metabolism in plants, and of the transformations of the carbohydrates 

 under the influence of acid, alkali, oxidation, and enzymes, and of the energy 

 relations of the products of these transformations. Then follows a description 

 of the methods employed. Opuntia phaeacantha and 0. versicolor furnished 

 material for the studies. In preparing the tissues for carbohydrate analysis 

 they were ground in a meat chopper and placed in an oven at 98 C. The 

 precaution of Davis and Daish of plunging the tissue into boiling alcohol 

 was not deemed necessary. The disaccharides and polysaccharides were 

 hydrolyzed by boiling with 1 per cent hydrochloric acid for 3 hours. All 

 sugar determinations were made voiumetrically with Fehling's solution. The 

 pentoses were determined after fermenting away the hexoses with bakers' yeast. 



The polysaccharides of the cactus are starch and xylan. The mucilage of 

 Opuntia consists of 34. 1 per cent d-glucose and 65 .9 per cent 1-xylose. Asso- 

 ciated with it there is probably an acid. Glucuronic acid was found as a con- 

 stituent of the sap. The formation of mucilage in special large cells could be 

 watched under the microscope under certain conditions. 



The relative abundance of the different groups of carbohydrates and also 

 of water is profoundly affected by the seasonal variations of the external 



8 Spoehr, H. A., The carbohydrate economy of the cacti. Carnegie Institution of 

 Washington. Publ. 287. pp. 79. 1919. 



