78 DIFFUSION AND OSMOTIC PRESSURE 



merely extra -cellular material. But Pf effer shows that there 

 is surely an extrusion of solutes from the stamens of Cynara. 

 It may be that all "sensitive" organs do not act alike in 

 this regard. Hilburg 1 states that the cells of the pulvini of 

 leaves of Phaseolus increase in turgor pressure when sub- 

 jected to the action of light. 



Puriewitch 2 found that absence of oxygen and the pres- 

 ence of anaesthetics prevented the giving off of reserve food 

 from cells of tubers, roots, bulbs, the endosperm of seeds, etc. 

 He explains this fact as an effect upon the diastatic enzymes 

 in the various cases, but the onion bulb and the beet root 

 exhibit the same phenomenon, and it is difficult to see how 

 organs whose stored food is already in solution could be 

 affected by an alteration in enzymes unless, indeed, even 

 sugars need to be modified by enzyme action before they 

 can pass the protoplasm. A live onion scale totally submerged 

 in water will give off no sugar, but if partially exposed to 

 the air exudation takes place. It is probable that here we 

 have another case of the influence of a chemical (i. e., 

 oxygen) upon the permeability of the membrane. That 

 enzyme action is necessary for the translocation of the cane 

 sugar of the beet root is possible and even probable. 



The permeability of the protoplast to a certain substance 

 may change according to the relative concentration of that 

 substance within and without the cell, as has been shown 

 recently by Nathansohn. 3 Codium tomentosum was used in 

 his experiments. The cells of this plant are permeable to 

 chlorids, so that the content of HC1 is found to be the same 

 in expressed sap and in the surrounding medium. If the 



1 C. HILBUKO, " Ueber Turgescenczftnderungen in den Zellen der Bewegungs- 

 gelenke," Unters. atts d. bot. Inst. zu Tubingen, Vol. I (1881), pp. 23-52. 



2K. PURIEWITCH, " Physiologische Untersuchungen u. d. Entleerung der Reser- 

 vestoffbehalter," Jahrb. /. wiss. Bot., Vol. XXXI (1897), pp. 1-76. 



3 A. NATHANSOHN, "Zur Lehre von Stoffaustausch," Ber. d. deutsch. bot. Ges., 

 Vol. XIX (1901), pp. 509-12. 



