64 



CARNEGIE INSTITUTION OF WASHINGTON. 



There is evidence, furthermore, that the growth-rates of pollen tubes are 

 hmited by their abiUty to make use of the sweUing effects of the acids in 

 question. At the higher concentrations at which growth may occur,burst- 

 ing of the tubes supervenes. At still higher concentrations, namely, above 

 N/3200, shrinkage, in amounts varying with the concentrations, occurs. 



With sodium hydrate it has been possible to find a point of concentra- 

 tions (ca. N/3200) , within the limits above mentioned, at which maximum 

 growth occurs. The parallelism of behavior between gelatine and the pro- 

 toplasm of pollen tubes when expressed in terms of accomplished growth 

 is therefore more apparent in the case of alkaline than of acid media. 



Experiments upon the hnhibitional Swelling of Marine Algce, by J. M. McGee. 



Since agar has been used in these laboratories as a basal carbohydrate 

 material in many mixtures prepared for the study of colloidal sweUing 

 and imbibition, it was thought advisable to investigate the swelling 

 of some of the red algse from which such material is derived, in various 

 solutions. The species which seemed most promising, because of 

 their form and their relationship, were Iridcea laminarioides, Gigartina 

 exasperata, and Gigartina mammillosa var. dissecta, all of which grow 

 on the rocks in Carmel Bay in large amounts. 



Trios of sections of the laminse of these species were swelled in 

 various solutions and their increase registered by the auxograph. 

 These marine algae have a normal balance enabling them to exist in 

 sea-water which contains about 3.50 per cent total salts. The effect of 

 the various substances on imbibition in these plants was therefore 

 obtained by adding them to sea-water in such quantities that they 

 formed hundredth-normal solutions. This practice made possible 

 comparisons with swellmg measurements made upon mixtures of agar 

 with various proteins, gelatine, etc., by Dr. MacDougal, the results 

 of which will be found elsewhere in this report. The potassium nitrate 

 and citric acid were used in a total hundredth-molar solution. 



The results of the swellings are as follows: 



Name of alga. 



Iridaea laminarioides: 



Tip of lamina 



Do 



Gigartina mammillosa var. dissecta: 



Tip of frond 



Do 



Lateral swelling 



Gigartina exasperata: 



Young lamina (fresh) 



Do 



Do 



Young lamina (kept 3 days) 



Thick- 

 ness. 



mm. 

 0.4 

 0.4 



0.5 

 0.5 



0.6 

 0.6 

 0.6 

 0.7 



Per cent swelling in — 



Sea-water 



plus NaOH 



N/100 





 25 



10 

 50 

 10 



33.3 



16.6 



12.5 



3.5 



Sea-water 



plus HCl 



N/100 





 31 



15 

 22.2 



58.3 

 20.8 

 50 

 7.1 



KNOsplus 



citric acid 



M /lOO 



537.5 

 175.0 



GO 

 60 

 17 



150 

 200.0 

 158.6 

 132.8 



