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JOURNAL OF THE ROYAL HORTICULTURAL 30CIETY. 



(8'5) are not markedly divergent. This fact shows that in this 

 respect these three conditions approximate most nearly the 

 normal state, i.e. in the open, in which the proportion of water 

 to dry substance is about 10 to 1 ; whereas under red glass 

 it is nearly 19 to 1, and under green glass a trifle over 12 

 to 1. 



Looking now to the causes of these results, and noticing the 

 mean temperature under each glass, it is clear that red glass 

 accumulates too much heat. This induces a greater amount of 

 respiration with a corresponding decrease of assimilative power, 

 which would seem to account for the diminished percentage of 

 dry substance.* On the other hand, while transpiration is aided 

 by the presence of the strong absorption-band No. I, yet this 

 process cannot keep pace with the absorption of water, the 

 amount of water being greatly in excess (94*8 per cent.) over 

 the amount in plants grown in the open (90 ,( J per cent.). 



Yellow and blue glass show more nearly equal effects than 

 in the case of adult Lettuces described below (pp. 73, 76). Now, 

 the temperatures under coloured glasses show one maximum 

 under red and yellow, and another under blue, because 

 a minimum occurs under green glass. Blue glass, therefore, 

 induces activities relatively similar to those under yellow glass ; 

 but they are inferior in absolute effects, as seen by the 

 column of total weights and the total amounts of dry substance. 

 This conclusion might be anticipated, as large chlorophyllian 

 absorption-bands (Nos. V, VI, and VII) occur in the blue, thus 

 supplying the energy necessary for the decomposition of carbon- 

 dioxide and water.f 



The fact that blue glass shows assimilative powers apparently 

 proportioned to respiration and transpiration, just as they are 

 under yellow and clear glasses, affords an interesting corrobora- 

 tion of the experiment for illustrating the evolution of oxygen ; 



* Bonnier, Mangin, and others have shown that respiration and 

 -assimilation are phenomena directly inverse of each other. Ann. des Sci. 

 Nat. 1870, p. 47. 



The above-named savants have also shown that annuals have two 

 periods of maxima of respiration, viz. at germination and when flowering. 

 The Mustard may be taken as illustrating the former, especially under red 

 Klass, while Virginian Stock represents the latter, in which the percentage 

 <»f dry substance is lower in the open than under clear glass, all the plants 

 being in full blossom in the former condition. See table, p. 70. 



| Sec Vines' Physiology of Plants, p. 15D. 



