INFLUENCE OF EXTERNAL CONDITIONS ON GROWTH 273 



Further examples of the effect of dissolved substances upon the permeability 

 of protoplasm may be found in the work of Demoore and Sziics. Demoore 1 

 found that the addition of peptone to a very weak solution of sodium chloride, 

 which itself had no injurious effect upon the cell, greatly increased the perme- 

 ability of the protoplasm. Sodium citrate neutralized this action of the peptone. 

 Sziics 2 showed that the addition of an electrolyte retards the entrance of basic 

 aniline dyes into the cell. 



Alterations in the turgidity of the cell, due to changes in the amounts of water 

 and of dissolved substances in the surrounding medium, are among the causes 

 that bring about changes of form in plants. The amount of water vapor in 

 the surrounding air influences the rate of plant transpiration, and the more water 

 is lost by transpiration, the more is absorbed from the soil, if the supply is ade- 

 quate. But plants absorb, along with water, the essential ash-constituents and 

 upon the latter depend, in turn, the formation and migration of various organic 

 substances. That the amount of water absorbed determines not only the ex- 

 ternal form and the internal structure of the plant but also its chemical compo- 

 sition, may be seen from the experiments of Schlosing. 3 He cultivated tobacco 

 plants under glass bell-jars and also in the open air. The dry weight produced 

 in the moist atmosphere in four weeks was 40 g., while that produced in ordinary 

 air in six weeks was only 29.4 g. The leaves of the moist culture formed and 

 accumulated more non-aqueous material. But this material of the moist culture 

 contained less ash; the ash content, in percentage of the total dry weight, was 13 

 per cent, for the moist culture and 21.8 per cent, for the culture in ordinary air. 



These analyses also show that the leaves of the moist culture of this experi- 

 ment differed in other ways from those grown under usual conditions. The 

 modified rate of transpiration affected also the formation of various organic 

 compounds. The following table shows the amounts of various substances 

 found by Schlosing in the leaves of his plants grown under the two sets of condi- 

 tions, the numbers representing percentages, on the basis of the dry weight of 

 the leaves. 



Moist Usual 



Conditions Conditions 



Urea 4 . 00 502 



Nicotin 1.32 2.14 



Other nitrogenous compounds 1 7 . 40 1 8 . 00 



Oxalic acid 0.24 6 . 66 



Citric acid 1.91 2.79 



Malic acid 4.68 9.48 



Pectic acid 1 . 70 4.36 



Cellulose 5 .36 8.67 



Starch 19 . 30 1 . 00 



1 Demoore, J., Influence du citrate de sonde sur les echanges cellulaires. Bull. Soc. Roy. Sci. M6d. 

 et Nat. Bruxelles, No. 4, p. 79-81. 1909. [Rev. by Micheels in: Bot. Centralbl. 116: 166. 1911.] 



2 Sziics, Josef, Studien iiber Protoplasmapermeabilitat. Ueber die Aufnahme der Anilinfarben durch 

 die lebende Zelle und ihre Hemmung durch Elektrolyte. Sitzungsber. (math, naturw. Kl.) K. Akad. Wiss. 

 Wien. 119': 737-773. 1910. 



3 Schlosing, 1869. [See note 1, p. 150.] [But for another study on tobacco, giving quite the opposite 

 conclusion, see: Hasselbring, 1914. (See note w, p. 150.) — Ed.] 



18 



