10 EFFECT OF SOLUBLE SALTS UPON" PLANTS. 



the presence of a coating of wax on the leaves, while the control 

 plants in every case retained their normal green color. 



A comparison under the microscope of sections of leaves from 

 plants grown in the saline soils with those of the controls showed 

 that the waxy deposit on the cuticle was strongly developed in the 

 former, but almost completely wanting in the latter. Bloom did 

 appear, however, to some extent on the leaves of the control plants 

 after the ground was allowed to become dry, indicating that the 

 formation of bloom can be stimulated by a lack of water in the soil 

 as well as by the presence of an excess of soluble salts. 



The bloom was present in equal amount on both the upper and the 

 lower surface of the leaf. 6 It appeared as a thin, almost homoge- 

 neous layer of waxlike substance which showed a slight tendency 

 to accumulate along the lines of junction of the outer with the 

 radial walls of the epidermal cells. A careful examination of the 

 areas over the stomata c showed that there was no greater accumula- 

 tion of bloom there than on any other portion of the leaf, the deposit 

 of wax on the outer walls of the guard cells and the cells adjoining 

 them being of uniform thickness with that overlying other cells/ 



a As to the origin of the bloom or wax on the leaves and stems of plants there are 

 many theories, some of which were advanced as early as 1827. De Candolle asserted 

 that the wax appears on the surface in the form of a liquid and is coagulated upon 

 exposure to the air. 



Karsten (Vegetationsorgane der Palmen) and ITloth (Ueber die "Wachsbildung in 

 Pflanzenreich, Flora, 1867, p. 422) sought to show that bloom originated through a 

 complete chemical change of the cuticle and other cell wall layers. De Bary, on the 

 other hand, contended that the bloom could not be the product of a modification of 

 the cell wall, but that the wax is secreted by the epidermal cells themselves. 



& Francis Darwin (On the Relation Between the "Bloom"' on the Leaves and the 

 Distribution of the Stomata. Journ. Linn. Soc. Bot., 22 : 99, 1886) found from a study 

 of different species of Trifolium that there is a close relation between the distribution 

 of the bloom and that of the stomata. "When the bloom is on the upper surface of the 

 leaf only, the average number of stomata on that surface (as compared with the lower) 

 is twice as great as where both surfaces are covered with bloom. 



c Wulff (Studien iiber verstopfte Spaltoffnungen, Oesterr. Bot. Ztschr., 48:201, 

 252, 298, 1898) made a study of the bloom on a large number of plants widely sepa- 

 rated in relationship and found the stomata in many cases covered with wax. He 

 states that while transpiration is largely reduced by means of the wax or bloom cover- 

 ing the stomata, assimilation still continues, and mentions in this connection Drimys, 

 Elymus. Papaver nudicaule, and other plants. 



Schleiden (Harmlose Bemerkungen iiber die Xatur der Spaltoffnungen, Xaturgesch., 

 J. 4, bd. 1, pp. 56-59, 1838) noticed that the stomata of some species of the conifers 

 were covered over with a wax, but does not mention Link, who observed the same 

 condition earlier. 



^De Bary (Ueber Wachsiiberziige der Epidermis, Bot. Ztg., J. 29, Xo. 9. p. 128: No. 

 10, p. 144; Xo. 11, p. 160, 1871) has made what is perhaps the most extensive study 

 of the deposition of wax on the stem and leaves of plants that has ever been carried 

 out. His observations include a large number of different species, as, for example, 

 Klopstockia cerifera, Panicum turgidum, Copernica cerifera, and Heliconiafarinosa. He 

 found the wax to be in many cases more abundant on the guard cells and the cells 

 adjoining them than on other portions of the leaf surface. 



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