Besearches in Vegetable Physiology. 147 



upon the production of starch in coloured light, and expresses 

 himself in opposition to the assertion of that author, that no 

 trace of starch is produced under the influence of the blue 

 rajs. 



M. Krauss has followed the experimental methods indicated 

 by M. Sachs, in seeking the smallest traces of starch in the 

 tissues, and employed, as a coloured medium, the large double 

 bells also invented by that eminent observer. The interval 

 between the two bells is filled with a solution of bichromate 

 of potash for the least refrangible part of the spectrum, and 

 with a solution of ammoniacal oxide of copper for the more 

 refrangible rays. 



Different Aquatic and terrestrial plants vegetated succes- 

 sively in these apparatus [Spirogyra, Funaria hygrometricM, 

 Elodea canadensis^ Lepidium^ &c.). The result was con- 

 stantly the saiue ; in the three bells employed (with white, 

 yellow, and blue light) starch was formed. The only differ- 

 ence between them was one of proportion and promptitude. 

 Thus in white light and in the sun the first traces of starch 

 were visible in five minutes ; in blue light, only an insolation 

 of several hours was capable of producing an appreciable 

 effect. 



The temperature also exerted a certain influence, but only 

 in the proportion in which it acts upon vegetation in general. 

 When the heat is greater, vegetation is more active, and it is 

 therefore very natural that a greater quantity of starch should 

 be produced. But this effect is not due to a direct interven- 

 tion of the caloric element in the phenomenon ; for tlie produc- 

 tion of starch, although very slight, is still appreciable at a 

 temperature at which most of the other functions are sus- 

 pended. 



A check experiment, made, by means of the balance, upon 

 cotyledons of Lepidium and Linum, showed, by a notable aug- 

 mentation of weight, that the starch was formed in them from 

 the elements, and that it was not a product of transformation. 



M. Prilleux* has taken up the idea that the effect attri- 

 buted by his predecessors to the refrangible rays themselves 

 was rather due to the diminution of the luminous intensity. 

 In the experiments of M. Famintzin upon Spirogyra^ he says, 

 the light which traverses the solution is so feeble that it is 

 incapable, by itself, of producing a marked effect. According 

 to this author, the assimilant faculty of the leaf is proportional 

 to the illuminating-power of the rays which it receives. 



* Comptea Rendus, 1870, tome Ixx. p. 521 ; Ann. des Sci. Nat. 5" s^r. 

 tome X. 



