636 SCIENCE PROGRESS 



the ratio between the number of grams of carbon dioxide 

 assimilated in one hour and the weight of chlorophyll 

 concerned, to which ratio they gave the name of assimilation 

 number. Experiments with normal, autumnal, and etio- 

 lated leaves showed that the assimilative effect is not always 

 proportional to the chlorophyll content, which is explained by 

 assuming that the process of assimilation is to some extent 

 effected by an enzyme, probably acting at the surface of contact 

 between the chloroplast and the plasma. The fact that in 

 leaves rich in chlorophyll an increase in illumination produces 

 no effect on assimilation, whereas a rise in temperature brings 

 about increased assimilation is explained by the accelerating 

 effect of a rise of temperature upon the enzyme action. In 

 the case of leaves deficient in chlorophyll a rise of temperature 

 has but little influence, whereas increased illumination has 

 a very marked effect. The explanation offered in this case 

 is that there is more than sufficient enzyme present for the 

 chlorophyll present, but that the greatest assimilative effect can 

 only be attained when all the chlorophyll is exerting its maxi- 

 mum activity. All attempts to bring about assimilation by 

 means of chlorophyll isolated from the leaf failed, in all proba- 

 bility owing to absence of enzyme. The removal of the epider- 

 mis from the undersurface of the leaves had no deleterious 

 effect on assimilation, whereas only a slight pressure applied 

 to the leaves brought assimilation to a complete standstill. 



The effect of plant nutrition upon chlorophyll production 

 has been investigated by Pollacci and Oddo (A Hi. R. Accad. 

 Lincei, 191 5 [v], 24, ii, 37). Comparative experiments with 

 seeds of Zea mats grown in nutrient solutions composed of 

 calcium and potassium nitrates, ammonium sulphate and 

 potassium dihydrogen phosphate with or without the addition 

 of a small quantity of the magnesium salt of pyrrole car- 

 boxylic acid showed that the seedlings grown in the presence 

 of the magnesium salt had their leaves at least three times as 

 well developed as the others and their colour was normal, 

 whereas the leaves of the others were ill developed and deficient 

 in chlorophyll. 



A new method for the classification and evaluation of 

 caoutchoucs is described by Ostromisslenski (/. Russ. Phys. 

 Chem. Soc. 191 5, 47, 1374). According to this author the 

 elastic property of caoutchouc and its property of vulcanising 



