68 CARNEGIE INSTITUTION OF WASHINGTON. 



for 1915, p. 66) that certain electrolytes can cause marked swelling 

 of the protoplasm, as of such emulsion colloids as gelatine. It must 

 be noted, however, that indirect effects may conceivably occur, such 

 as changes induced in the stiiicture of the cell-wall, and these must 

 not be overlooked. 



Acids (hydrochloric, nitric, acetic, citric), in concentrations within 

 the range N/200 to N/51200 inclusive were found in no case to increase 

 the growth-rate when combined with 20 per cent cane sugar. At the 

 lower concentrations the rates were approximate or equal to the con- 

 trol. At the higher (N/200 to N/1600), growth was less and less, and 

 bursting took place most quickly in the highest concentrations. 

 When, however, acid (acetic) is combined with cane sugar in a con- 

 centration of 40 per cent, in which, in the absence of acid, growth 

 occurs only slightly, the maxunum growth (four times that of the con- 

 trol) occurred in the concentration N/6400 of the acid component. It 

 seems clear that the acid increased the imbibition pressure of the 

 living colloids sufficiently to enable them to overcome the contrary 

 effect of the cane sugar— a form of antagonism not hitherto recognized. 

 Concentration below N/6400 produced less growth, while those above 

 caused bursting. 



Of the alkalies, the effect of sodium hydrate has been studied. In 

 combination with 20 per cent cane sugar, the rate of growth is greater 

 at the concentrations N/800 to N/1600 than in the control and than 

 in other concentrations. In the higher concentrations bursting occurs. 

 That growth takes place in concentrations of alkali lower than acid 

 may be due to the probably already present acid of the protoplast or 

 to the possibility that the alkali acts merely on the outer protoplasmic 

 membrane or on the cell-wall. Sunilar concentrations in water cause 

 bursting, and the ready penetration of sodium hydrate has been shown 

 to occur by means of neutral red. The result obtained, therefore, 

 can hardly be referred to effects on the membrane alone, though it has 

 been found, especially in the case of Lupinus pollen, that certain concen- 

 trations cause, in the absence of increase of growth of the protoplast, 

 an excessive deposition of cellulose, especially within the apex of the tube. 

 It is also evident that the failure of acids to cause increased growth 

 in the presence of 20 per cent cane sugar is not due to poisonous effects, 

 since the tubes remain alive, and since, at higher concentrations of sugar, 

 growth actually takes place in excess of that in the control. 



In addition to the excessive deposition of cellulose the shape of the 

 pollen-tube may be affected. In general, the tube tends to become 

 bulbous, or even spherical, under conditions which increase the imbibi- 

 tion of the contained protoplast. 



The investigation of a typical salt (potassium nitrate) in similar 

 combination with cane sugar gave no increased swelling and no increased 

 growth-rates. 



