DEPARTMENT OF BOTANICAL RESEARCH. 63 



Colloidal Phenomena in the Protoplasm of Pollen Tubes, by Francis E. Lloyd. 



The study of the swelHng rates of gelatine at various concentrations 

 of acids and alkahes has been continued in order to throw light on the 

 behavior of pollen tubes grown in such reagents in the presence of 

 high constant concentrations of cane sugar. The results are briefly 

 summarized as follows: 



Within the limits of concentration N/10 to N/2560 of the reagent 

 (acid or alkali) the maximum swelling rates and maximum total swell- 

 ing in acids occur at N/10 (malic acid) to N/320 (hydrochloric acid) 

 and for alkalies at about N/80. The organic acids cause maximum 

 swelling at higher concentrations than the mineral acids, apparently 

 in direct relation to the degree of dissociation. It is also to be noted 

 that the maximum swelling rates during the earlier periods occur in 

 higher concentrations than later, the movement of the high point of the 

 curve being greater for mineral than for organic acids. It may be sug- 

 gested that this results from the partial adsorption of the acid by the 

 gelatine, with consequent dilution and greater dissociation of the 

 remainder of the reagent. There is a similar but less movement of 

 the maximum rates of swelling in alkalies. 



At lower concentrations of acids and alkalies there is a repression of 

 swelling rates, especially in hydrochloric acid, as observed by Proctor 

 (Jour. Chem. Soc. London, vol. 109-110). This is always greater for 

 acids, the repression being sufficient to lower the rates materially 

 below that for water, while in alkalies the rates are about equal to or 

 only slightly less than that in water. The concentrations in question 

 range below N/640, the minimum rates found being, e. g., for sulphuric 

 acid N/1280, for hydrochloric acid N/2560, acetic acid, N/640, formic 

 N/1280 (temp. 20° C.) . During the later period of swelling the repres- 

 sion may or may not be overcome, it being permanent in acids and 

 transient in alkalies. With the above facts in hand, it has been sought 

 to determine how far a paralleHsm is to be found between the behavior 

 of protoplasm in pollen and that of gelatine. 



Proceeding from the results previously attained (Carnegie Institu- 

 tion Year Book for 1916, p. 67), the effects of a seiies of acids (hydro- 

 chloric, acetic, malic, citric, formic, and oxalic) have been determined 

 for concentrations N/200 to N/25,600 in association with cane sugar 

 in concentration of 16 per cent. 



In these solutions no growth occurs at concentrations at or above 

 N/3200 of the acid component. Below that limit the rate of growth is 

 inversely as the concentration. The rate and total amount of growth 

 possible for any concentration ^"aries with the acid, it being least at 

 the higher concentrations for formic and oxalic and highest for acetic. 

 It will be noted that these concentrations are very much lower than 

 those dealt with by Long, MacDougal, and Spoehr, in stud}dng acidity, 

 respiration, and swelling in cacti and in biocolloids. 



