112 Agricultueal Experiment Station, Ithaca, N. Y. 



would filter out at the other. The protoplasmic utricle* -which lines 

 the cell wall is not permeable, or at least only to a small degree. The 

 water, then, which passes into the cell through the protoplasmic utricle, 

 cannot filter out, and when it does not escape by evaporation or exos- 

 mose from the surface, it stretches the protoplasmic utricle, presses it 

 against the elastic cell wall which then yields and the cell is turgid. 

 The extent to which the cell wall is stretched depends upon the endos- 

 matic activity which introduces water into the cell, the rate of trans- 

 piration and the firmness of the cell wall. The endosmatic activity 

 within the cell is brought about by the presence of certain salts or 

 organic acids in the cell sap, which have a strong afiinity for water.f 



By root absorption the plant is supplied with water, the permeable 

 cell wall permitting it to flow from the vascular bundles into the 

 fundamental and other tissues, where it comes in contact with the pro- 

 toplasmic membrane lining the cell wall. When root absorption is 

 active and transpiration is inactive or at a low ebb, the affinity which 

 the vegetable acids possess for the water draws it within the cells. 

 Root absorption practically being in operation continuously under the 

 conditions of the forcing house, the transpiration being in operation 

 for such a large part of the time, the cell walls are unduly stretched. 

 This continues until a point is reached where normal tissue tension of 

 the leaf or the cortical parenth^mia of the stem is no longer held in 

 longitudinal tension. The cell wall thus continuing to stretch yields 

 at the point of least resistance which is at the surface of the congested 

 tissue and the radial elongation of the cells is the result. 



*Mohl. Bot. Zeitung, 1846, p. 75. 



Nsegeli, Pflanzenphyeiologische Untersuch, Heft I, 1855, p. i. 



Pfeffer, Osmotische Untersuchungen. Leipsig 1877. 



SacliH' Physiology. 



Goodale, Physiological Botany. 



f De Vries, Ueber die Ausdehnung wachsender Pflanzenzellen durch ihren 

 Turgor, Vorlaufige Mittheikmg; Bot. Zeit. 1877, S., 1-10. 



Untersuchungen iiber die mechanischen Ursachen der Zellstreckung von der 

 Einwirk von Salzlosungen auf den Turgor wachsenden Pflanzenzellen, Leip- 

 sig, 1877. See Justs Bot. Jahresb. 1877, I, p. 65-67. 



Ueber die Beduetung der Pflanzensiiuren fijr den Turgor der Zellen. Bot. 

 Zeit. 1879, p. 847. 



Palladin, Hthmung und Wachsthum, Berichte d. Deutsch. Bot. Geesell- 

 schaft, 1886. pp. 322-328. 



Bildung der organischer Siiuren in den Wachsenden Pflanzentheilen, Ber. d. 

 Deuts. Bot. Gesellschaft, 1887, p. 825. 



