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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Comparing the final total weights, we see how that under red 

 (20*3 grs., Table I. col. 1) it is considerably more than under 

 green (15-7 grs.), and exceeds that under blue (24*9 grs.). Now, 

 looking at the first column of Table II., we find that the dry 

 .substance under red falls short of that under blue. Reducing 

 the dry substances to percentages, a still more important differ- 

 ence is seen, in that under red it is only 7*1 (Table II. col. 4), 

 but under blue it rises to 10*0. Hence it appears that, while red 

 glass favours total weight, blue glass is really more favourable 

 for healthy assimilation, as there is a greater accumulation of 

 water in the tissues under red glass. 



The marked difference in the percentage, as shown in 

 -col. 4, is, of course, due to the larger amount of water in 

 plants grown under red glass than in those under blue. This is 

 seen in col. 4 of Table III., where the percentage is nearly 93 

 for the former and about 89 for the latter. 



With regard to the absorption of water by plants grown under 

 red glass, although it gives, as I have elsewhere shown,* one 

 maximum of transpiration, there must be some powerful cause 

 to account for the large percentage of water present, notwith- 

 standing the great loss due to this function. A presumable cause 

 is heat, as temperature is not directly concerned in transpiration. 

 Organic acids, however, have been proved by H. de Yries to be 

 an essential feature in turgescence. The question then arises 

 whether heat alone stimulates the absorptive powers to an ex- 

 cessive degree, or whether it is indirectly a cause of turgescence 

 by bringing about the production of organic acids which cannot 

 be further decomposed in the absence of other rays.t 



Considering next the effects of green glass which exhibits the 

 least amount of vital activity in plants growing under it, we find 

 first that the total increase of weight is the least of all, or 5*7 grs. 

 (Table I. col. 2). The weight of drysubstance actually decreased 

 as compared with the original amount by calculation from 

 the initial stage, viz. from 1 gr. to 083 gr. (Table II. col. 1), 

 while the amount of water in the tissues increased from 9 grs. 



* "A Contribution to the Study of the Relative Effects of Different Parts 

 of the Solar Spectrum on the Transpiration of Plants, " Journ. Linn. Soc. 

 Hot. xxii. p. 81. 



t See a paper by M. H. .Tumelle, "Recherches Physiologiques sur le 

 derelo ppemsnl dee Plan tea Annuelles," Hev. Gin. dc Dot. torn. i. p. 389. 



