57 8 SCIENCE PROGRESS 



associated with increase of polysaccharides, decrease of 

 monosaccharides, and increase of pentosans. 



(2) High water content and low temperature are 

 associated with decrease of polysaccharides, increase of 

 monosaccharides, and decrease of pentosans. 



The rate of respiration was found not to be definitely 

 controlled by any one group of sugars. The hexose mono- 

 saccharides which have been most commonly supposed to be 

 closely concerned in respiration are at times only present in 

 very small amounts, but the rate of respiration is not markedly 

 reduced. It would seem, therefore, that under conditions of 

 stress the plant utilises polysaccharides in respiration, and 

 Spoehr thinks that the formation of pentosans is in connection 

 with this condition. In the case of the polysaccharides the 

 carbonyl group — CH:0 is not the first point of attack, but the 

 sugars are first affected at the opposite end of the chain of car- 

 bon atoms, i.e. at the — CH 2 OH group. Such a reaction results 

 in a primary formation of glucuronic acid,CH:0(CHOH) 4 -COOH, 

 and this substance Spoehr has isolated definitely from the 

 cactus. This is the first time that glucuronic acid has been 

 reported as a plant constituent, though it has been found 

 as a product of glucose metabolism in mammals. From 

 glucuronic acid we should expect the formation of /-xylose, 

 a pentose sugar, under the action of sunlight. In support of 

 this conclusion of Spoehr's as to the origin of pentosan in the 

 plant under conditions in which the plant utilises disaccharides 

 or polysaccharides in respiration, it may be observed that 

 if pentoses were derived from a direct oxidation of 

 hexoses, ^-glucose would yield d-arabinose and ^-galactose give 

 d-xylose, whereas in nature d-glucose is found with /-xylose 

 and ^-galactose with /-arabinose. 



ZOOLOGY. By Prof. Chas. H. O'Donoghue, D.Sc, F.Z.S., University 

 of Manitoba, Winnipeg, Canada. 



Protozoa. — Hegner gives an account of the " Heredity, Variation, 

 and the Appearance of Diversities during the Vegetative Repro- 

 duction of Arcella dentata " (Genetics, vol. iv, March 191 9). This 

 records the results of a study of the breeding of the protozoon 

 mentioned, and is concerned particularly with one largefamily 

 °f 5»S57 individuals, direct descendants of one original speci- 

 men, and produced in the course of 69 generations of asexual 

 reproduction. The species was chosen because it presented 

 two characters — i.e., the diameter of the shell and the number of 

 spines on it — that are suitable for mathematical treatment, 



