GROWING PLANTS UNDER GLASSES OF VARIOUS COLOURS. 77 



to be acquired, because the accumulation of water is so much 

 less ; while respiration is probably also reduced. 



Moreover, under red, yellow, and green coloured light there is, as 

 stated, a tendency to elongate the axis ;* but this does not occur 

 under blue light, which in this respect resembles white or clear light 

 as well as plants when grown in the open without any glass at all. 



The arrest of the axis under blue glass is also correlated with 

 the smaller amount of water in the tissues, for excepting plants 

 crown under clear glass and in the open the percentage is the 

 least— 89*4 (Table IV. col. 4 ). 



Lastly, of the results obtained from plants grown in the open, 

 by comparing them with the preceding we get marked differences, 

 which can presumably be only attributed to a lower temperature 

 than that under clear glass, coupled perhaps with a diminished 

 circulation of air. 



The total increase of weight of the plants grown in the open 

 has risen by 673 per cent., as compared with 447 per cent, for 

 those under clear glass. 



By comparing the numbers corresponding with plants grown 

 in the open with the rest, it will at once be seen that the latter 

 are greatly at a disadvantage — that nothing is gained by growing 

 them in any way except freely exposed. 



If it be thought it would be advisable to make Lettuces more 

 succulent by growing them, say, under green glass, then the table 

 of total weights reveals the fact that they fail to produce quantity, 

 and at the same time the axes are encouraged to elongate and 

 not the foliage to expand. 



There is one more general result to be noticed, which is 

 revealed by the columns 3 and 4 of Table IL In the young 

 stage, when the seedlings were first planted, the assimilative 

 powers were only capable of producing 10 per cent, of dry sub- 

 stance. Under red, yellow, and green glasses this assimilative 

 capacity subsequently decreased ; while under blue and clear 

 glasses, and above all in the open, the assimilative powers 

 greatly increased with age. 



An important question appears to arise from the preceding 

 observations, namely, in whit way do the different 'rays assist 



* Under red, the stem was 10 inches ; under yellow, 10 inches ; under 

 jrreen, tih inches ; under blue ar d clear glass, as w^ll as in the open, it was 

 about 3 inches. 



