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THE POPULAR SCIENCE MONTHLY. 



tie this question ; among them the following : A forked branch of lilac 

 (Fig. 1) was so disposed that the one branch was immersed in water, 

 while the other was exposed to the ordinary atmospheric conditions. 

 The superficies of foliage was the same on both branches. The transpi- 

 ration from the surface of the leaves on the latter branch was the same 

 as under normal circumstances, and after the lapse of two weeks the 

 foHage was as fresh as at the commencement, showing that the sub- 

 merged leaves were fully able to replace the roots in one of their func- 

 tions. In an experiment with a beet in which one-half of the leaves 

 were in water and one-half in the air, communication being maintained 

 by means of the root, the free portion of the leaves Avilted in the course 

 of a day, the neck of the root apparently not offering a sufficient means 

 of communication with the submerged leaves A grapevine shoot half 

 plunged in water (Fig. 2) maintained a normal evaporation in the free 

 foliage, and remained fresh for over a month. An oleander shoot under 

 similar conditions maintained its normal appearance for four months. 

 With the artichoke it was found necessary that the surface of the leaves 

 beneath the water should be four times that of the leaves above. 



Closely bordering on this question is another which has excited 

 much dispute, viz., the ability of leaves to draw water from the sur- 

 rounding air or by immersion, after having suffered losses by transpira- 

 tion. Prof. Boussingault's numerous experiments show that leaves, 

 after having been exposed to influences causing a rapid evaporation, 

 are able to absorb water rapidly on immersion, and even from an atmos- 

 phere saturated with aqueous vapor. There is, however, in both cases 

 no absorption unless the leaves have lost a portion of their water of 

 constitution, i. e., that which is essential to their normal existence. 

 Thus, a wilted branch of periwinkle weighing 4 grammes, after re- 

 maining in an atmosphere saturated with aqueous vapor for a day and 

 a half, weighed 4'2 grammes, and after twelve hours' immersion in 

 water 9'4 grammes. 



Fig. 3.-4, drop of solution ; B, watch-glass. 



The last function of leaves studied by Prof. Boussingault is their 

 ability to absorb solutions of mineral matter, i. e., perform another of 

 the ordinary duties of the roots. For this purpose a solution of gypsum 

 containing ^ q-„ q- of solid matter was used. Drops of this solution were 

 placed on the leaves of a great variety of plants — under conditions fa- 

 voring absorption, as in the experiments just described — and protected 



