414 SCIENCE PROGRESS. 



in feeble light the spongy will appear to advantage as the 

 assimilating tissue, and the greater number of starch grains 

 will then be formed in its cells. 



Till Wortmann's objections are rebutted by experiment, 

 Pick's conclusions, that red light, as such, facilitates the 

 translocation of carbohydrate material — and this by increas- 

 ing the activity of the diastatic ferment — cannot be accepted. 

 Pick's experiments however have to be reckoned with in 

 any attempt to discuss the question of the functions of 

 anthocyan; and it is now to be shown how Stahl harmonises 

 them with experiments of his own and gives to them a 

 simple interpretation. 



In an important paper which appeared last year in the 

 Buitenzorg Annals, Stahl (29) discusses with considerable 

 fulness this anthocyan question, and brings experimental 

 evidence to show that some of Kerner's hypotheses are, in 

 all probability, correct. 



The main fact which he establishes is that members, rich 

 in anthocyan, have peculiar thermal properties, and that 

 these supply the key to the solution of the problem in 

 hand. 



Kny i^-^o) had demonstrated that the temperature of the 

 water in a vessel filled with red leaves rose hicrher than that 

 of water in a similar vessel containing green leaves ; and 

 Stahl obtains similar results, using the expressed sap of red- 

 leaved Begonias. By more delicate experiments he fully 

 confirms this heat absorption of anthocyan. In some ex- 

 periments he uses a delicate thermopyle whose spathulate 

 electrodes can be buried to any required depth in the leaf 

 tissue ; in others he measures the rate at which a thin layer 

 of coco-butter melts from the different colour areas of a 

 given particoloured leaf. His sources of heat are, in some 

 cases, a gas burner, in others, a Leslie cube by which 

 dark heat only can be used. In all cases he finds, in 

 red-spotted leaves, that the red areas become warmer 

 than the non-red when the leaf is exposed to a source of 

 light or dark-heat. 



These results Stahl applies to the interpretation of 

 various phenomena observed by Kerner and Pick. Thus, 



