36 PLANT PHYSIOLOGY 



126, 1. 39, for TIMIRIASEF (1885) read TIMIRIASEF (1885, 1903), 



127, 11. 10-12, for with the ... be thrown read for instance, with the gas- 

 bubble method, or in carrying out eudiometric researches, or in estimating the 

 amount of starch formed ; on the other hand a microscopic spectrum may be 

 thrown 



1. 28, after points read of agreement 



1. 33, after to us. read That ultra-violet light has also a feeble power in 

 this respect is asserted by BONNIER and MANGIN (1886) only. 

 ^35. f or beyond read beside 



I. 39 P. 128, 1. 10, for On the other hand . . . assimilation read 3. The 

 principal apex of this curve lies in the less refrangible half of the spectrum. 



Different views are held, on the other hand, as to the questions (i) in 

 what wave-length region this chief maximum lies, and (2) whether, in addition, 

 there is a second maximum in the region of less wave length. We will deal 

 with the second question first. 



If a plant be placed under a double-walled bell- jar filled with potassium 

 bichromate or with ammoniacal cupric oxide, which allow yellow and blue 

 light to pass through respectively, one sees that the plant assimilates almost 

 as well in the yellow light as in white light, but only very feebly in the blue 

 light. The experiment is more accurate if one dispenses entirely with absor- 

 bent glass vessels, and uses REINKE'S spectrophore. When the light, by its 

 means, is spectrally divided, first the less refrangible rays (up to line D), 

 and then the more refrangible ones, are severally concentrated by means of 

 a biconvex lens. In this way one can subject the plant to the influence of 

 either red or blue light. All authors are agreed that the red half has much 

 greater effect than the blue. TIMIRIASEF (1903) states that the former has 

 twice the assimilatory activity of the latter. One fact of great importance is 

 established from these experiments, viz. that the light rays that play the chief 

 part in CO 2 -assimilation are other than those which induce the decomposition 

 of silver salts. To describe, therefore, the blue-violet rays which are effective 

 in the case of silver salts briefly as the ' chemically active ' rays is a quite 

 erroneous generalization. 



According to some authors (especially REINKE, 1884) the curve of assimila- 

 tion continuously sinks in the course of the blue half of the spectrum, while 

 according to ENGELMANN (1884) a second maximum is attained near FRAUN- 

 HOFER'S line F (comp. Figs. 27 and 28) ; this second maximum ENGELMANN 

 demonstrated by means of the bacterium method, but PFEFFER (Phys. I, 

 p. 345), on repeating the experiment with the same method, was unable to 

 confirm this observation. KOHL (1903) has more recently studied the same 

 question ; and from his experiments it may be concluded that although assimi- 

 lation still occurs near line F, there is no second maximum then. Earlier 

 statements of the same author (1897) appear to be even less securely founded. 



128, first column of table, for upper side read under side directly illumi- 

 nated ; and for lower side read upper side in transmitted light 



129, 1. 3, for why read in relation to which 



II. 35-40, for If relations . . . evidence, read Although then relations do 

 exist between absorption and assimilation, still these are very complex and 

 have yet to be made out in detail. A reinvestigation of this question is all the 

 more desirable as other, partly biological, considerations have been put for- 

 ward in support of a relation between absorption and assimilation. Thus 

 ENGELMANN (1884) has made some interesting statements with regard to the 

 non-green Algae. Since water absorbs the rays of greater wave length more 

 rapidly than the blue ones, the rays of shorter wave length are more and 

 more prominent (in the deeper layers of the sea). The colouring matters of 



