TUEGIDITY 71 



presence of the substance in question is due to digestion 

 outside the body, brought about by outward diffusion of 

 enzymes. 



Dandeno' has recently shown that inorganic salts are 

 absorbed in some instances by ordinary leaves when these 

 are kept covered by a solution by means of a constant spray, 

 or by submersion. This occurred to such a degree in this 

 writer's experiments with Thunbergia that plants of this 

 form whose roots were supplied with nothing but water, but 

 whose leaves were sprayed with a solution, were able to 

 make a good growth. Control plants, which had distilled 

 water applied to the leaves as well as to the roots, perished 

 in a much shorter time. Also, drops of solution placed upon 

 various leaves were completely absorbed if too rapid evapora- 

 tion was prevented. This observation has been mentioned 

 under c). 



g) Outward permeability. — Many substances which pene- 

 trate the cell from without have been shown to pass in the 

 opposite direction with equal ease. This has been especially 

 emphasized by Overton^ in the case of the soluble alcohols, 

 etc. But in general the outward passage from the plant 

 body of sugars and the various organic food substances has 

 not been demonstrated. It must be of rather rare occurrence, 

 or the phenomena of nutrition, etc., would be impossible. 

 There are, however, certain cases where exudation occurs, 

 notably in the case of glandular structures, both in plants 

 and animals. Laurent,' however, has demonstrated an out- 

 ward passage of enzymes (e. g., amylase and sucrase) from 



IJ. B. Dandeno, "An Investigation into the Effects of Water and Aqueous 

 Solutions of Some of the Common Inorganic Substances on Foliage Leaves," Trans. 

 Canad. Inst., Vol. VII (1901), pp. 238-350. 



2 E. OVEETON, " Ueber die osmotischen Eigenschaften der lebenden Pflanzen 

 und Thierzelle," Vierteljahrschr. der Naturf.-Ges. in Zurich, Vol. XL (1895), pp. 

 159-84. 



3 J. Laueent, " Snr I'exosmose de diastases par les plautules," Compt. rend., 

 Vol. CXXXI (1900), pp. 848-51. 



