302 SCIENCE PROGRESS 



Howe. In spite of its unpromising title this is an excellent and 

 exhaustive memoir on the distribution, origin, and economics 

 of kaolin, and is enriched by a valuable appendix on micro- 

 scopical methods of investigating this substance by Allan B. 

 Dick. 



BOTANY. By F. Cavers, D.Sc, A.R.C.Sc. 



Plant Physiology. — Considerable progress has recently been 

 made in the investigation of the oxidising ferments or oxidases 

 of plants, and it appears probable that the relation of these to 

 reducing ferments (reductases) and of both to respiration will 

 prove to be essentially the same as in animals. In a series of 

 papers Atkins (Set. Proc. Roy. Soc. Dublin, 15) has reported the 

 occurrence of oxidases and of inhibiting bodies in a large 

 number of plants, but two groups of tissues are apparently 

 free from oxidases — tissues markedly acid in reaction and 

 tissues containing large amounts of reducing substances. 

 Reed (Bot. Gaz. 59) points out that if oxidases play the essen- 

 tial role in respiration which has been attributed to them they 

 must be present in all living cells, and he has succeeded in 

 demonstrating their presence in a considerable number of 

 algae, as well as in acid tissues, by using more delicate methods 

 of detection and by testing acid tissues in such a way that the 

 acid juice and the ferment were kept apart. Ewart {Brit. 

 Assoc. Rep.) points out that such terms as peroxidase, catalase, 

 tyrosinase, applied to oxidase enzymes, are objectionable since 

 they indicate only one of the many reactions of these bodies ; 

 also that the distinction usually drawn between the oxidase 

 and peroxidase classes of ferments is unjustifiable, their sup- 

 posed fractional precipitation with alcohol being merely the 

 result of attenuation. He finds that organic oxidases are pro- 

 teins, with or without metals in basic or acid combination, 

 and that organic oxidases, like inorganic ones, vary only in 

 degree of strength — the strong will cause direct oxidation from 

 the oxygen dissolved in aqueous solution, the weak will only 

 transfer oxygen from labile oxygen compounds such as hy- 

 drogen peroxide or will use dissolved oxygen only in presence 

 of sensitisers like sodium chloride. He suggests that the 

 sodium chloride always present in plant-ash may not be a 

 useless constituent, but may exert a stimulatory or controlling 

 action on metabolism in connexion with special oxidation or 



