GROWING PLANTS UNDER GLASSES OF VARIOUS COLOURS. 



07 



The first fact noticeable is that plants become perfectly green 

 under light of all colours, showing that no glass used was of so 

 deep a tint or intensity as to cause the least etiolation or prevent 

 assimilation. 



Next, with regard to the results given in the table, it will be 

 observed that the differences in the total weights acquired do 

 not necessarily at all correspond with the respective total weights 

 of dry substance ; which latter, of course, is the best measure of 

 the assimilating powers of the plants under each kind of light. 

 Thus the total weight under yellow glass is 48-G7 grammes, 

 under green 37'80, and under red 41*52 grammes. Yet the 

 amount of dry substance under yellow is double that under red, 

 and one and a half times that under green.* 



Turning next to the column of gains in dry substance over 

 the amount in the embryos (the testas, of course, taking no part 

 in germination), it appears that yellow is the only coloured glass 

 which permitted of a sufficient amount of assimilative power to 

 overrule the waste due to respiration, so as to leave a relatively 

 considerable gain. As under red, green, and blue, there was a 

 minimum gain in the weights of dry substance. The gain under 

 clear glass, it will be observed, is far in excess, or about double 

 that under yellow, and approximates that under normal condi- 

 tions, or in the open. 



Reducing the amounts of dry substance and the correspond- 

 ing amounts of water to percentages, interesting results are 

 obtained. Thus red glass brings about the storage of the largest 

 amount of water, which necessitates the least amount of dry 

 substance. f The next result observable is that the marked 

 differences between the gains of dry substance under yellow, blue, 

 and clear glasses disappear, so that the percentages of dry 

 substance produced by yellow (8*8), blue (8*0), and clear glass 



* This implies a different distribution of dry substance over the plants 

 respectively, in correlation with different amounts of water. 



t Percentages may be regarded as affording the "net results" of 

 assimilation ; for they represent the actual amount of dry substance in the 

 plant, i.e. the " balance " or difference left between what is assimilated and 

 what is lost by respiration. Similarly the percentage of water represents 

 the residuum between absorption and transpiration. 



The fact that these four processes are all going on together at different 

 rates at different times and periods of growth, varying with different 

 luminous and thermic vibrations, shows how extremely complicated are the 

 collective phenomena, and the corresponding difficulties in any attempt to 

 attiibute the due effect to each process respectively. 



f2 



