412 SCIENCE PROGRESS. 



In passing, it is interesting to note that Engelmann sees 

 in these facts a confirmation of his important assertion that 

 the amount of assimilation effected by light of a certain 

 wave-length is proportional to the degree in which that 

 wave-length is absorbed by chlorophyll ; and he draws 

 attention to the fact that the above observations do not so 

 well fit in with the older view that the maximum assimila- 

 tion is effected by yellow light, in as much as anthocyan 

 effects some considerable absorption of that light. As 

 to the positive significance of anthocyan, Engelmann is 

 silent. 



A paper by Pick (26), dealing specially with the 

 significance of the red-colouring matter of Phanerogams, 

 has given rise to much discussion. This author confirms 

 Engelmann as to the absorption spectrum of anthocyan and 

 finds that the nearest approach to a substitute for the red 

 sap is afforded by a solution of alum-carmine and next by 

 ruby glass. Pick concludes from his experiments that 

 the red colouring matter of -leaves has the function of, 

 in the highest degree, facilitating carbohydrate transloca- 

 tion, without interfering with the assimilatory activity of 

 chlorophyll. This function of anthocyan may be conceived 

 to be of great importance. For, from experiments of Sachs 

 (27) and others, it is known that in many plants the amount 

 of carbohydrate manufactured by the leaf during the 

 day is in excess of the amount which diurnally passes as 

 sugar from the leaf. The carbohydrate not immediately 

 translocated takes the form of starch and as such is stored 

 by the leaf This residue of the carbohydrate manu- 

 factured daily is, during the night, converted by diastase 

 into sugar and in this condition passes from the leaf In 

 places subject to very cold nights this nocturnal work is 

 liable to be both dangerous and ineffectual ; dangerous 

 since it may prevent the protoplasm of the leaf from passing 

 into a resting condition when low temperature would do 

 comparatively little harm ; ineffectual since at low tempera- 

 tures translocation goes on more slowly than at higher. 

 Hence the great value of anthocyan, assuming Pick's 

 description of its properties, consists in its power, by 



