PRINGSHEIM^S RESEARCHES ON CHLOROPHYLL. 119 



of carbon in the plant if the absorption of the blue rays only- 

 en feebled respiration without directly affecting assimilation. 



Another outcome of the absorption in the chlorophyll 

 colouring matter is, that the maximum activity in the 

 spectrum for assimilation cannot be the same for all plants 

 and for all brightnesses, but being dependent on the depth of 

 colour of the plant and on the total intensity of illumination 

 its position must change with both conditions. Herein may 

 be found an explanation of the varying determinations which 

 have been given of the course of the- assimilation-curve in 

 the spectrum. 



3. The constancy in volume maintained in an atmosphere 

 in which green plants are growing has been looked to as 

 affording a clue to the chemical origin of the carbon-com- 

 pounds produced in assimilation. The primary assimilation- 

 products, it has therefrom been assumed, are directly derived 

 from the carbonic acid and water in the reducing-process, 

 the carbon of the former combining with the elements of water 

 to form a carbo-hydrate whilst the oxygen is given off. And 

 as anatomical evidence in support of this, the existence of 

 starch in the chlorophyll-corpuscles, as well as the fancied 

 physiological importance and distribution of glucose, have 

 been quoted. The, at present, comm.only received theory of 

 assimilation then, which considers starch and sugar as the 

 primary products of the process as opposed to the older one 

 of Liebig that they are organic acids, is founded upon such 

 considerations of gas-interchange supported by anatomical 

 facts. 



But although assimilation-theories are based upon this 

 assumption (it may be noted in passing, how completely 

 the nitrogenous constituents of the chloi'ophyll-corpuscles 

 are shut out from any influence in the process, and there is, 

 indeed, at present no reason for supposing that they have 

 any), it is not a necessary consequence. Any such conclu- 

 sions drawn from the constancy of the gas volume in gas- 

 interchange would hold if green organs only assimilated 

 and did not respire in light. But with respiration taking 

 place the conditions must be different, because oxygen is 

 thereby inhaled, and although this oxygen enters into com- 

 binations, one of the products of which is carbonic acid, yet 

 the volume of the gases in this interchange are not equal. 

 More oxygen is inhaled than carbonic acid exhaled. Germi- 

 nating seeds rich in starch cannot, as has been pointed out, 

 be simply or fairly compared with green organs of adult plants 

 in respect of their respiration, but in germinating oily seeds 

 more oxvgen is evidentlv inhaled than carbonic acid exhaled; 



