28 Hydration and Growth. 



Trios of sections of the laminae 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-molar solu- 

 tions. The results with Iridoea laminarioides were as follows at 16° C. : 



Table 8. 



Thickness, 0.4 mm. p. d. 



Sea-water + NaOH, 0.01 M 25 



Sea-water + HCl, 0.01 M 31 



KNOi -f- citric acid, 0.01 N 176 



Young fronds of Gigartina exasperata gave average swellings as 

 below at 16° C: 



Table 9. 



p. ct. 



Sea-water, sodium hydroxid, . 01 M 28 



Sea-water, hydrochloric acid, . 01 M 38 



Potassium nitrate, citric acid, . 01 N 142 



Such reactions are indicative of a high proportion of amino-acids, 

 which probably fell off toward maturity, and which may have been 

 extracted by washing as sections which had been treated with distilled 

 water, a treatment which would result in the extraction of some of the 

 salts and the amino-acids. Such sections when dried to a thickness 

 of 0.5 mm., gave swellings at 16° C. as follows: 



Table 10. 



p. ct. 



Distilled water 4,331 



Hydrochloric acid, 0.01 M 2,967 



Sodium hydroxid, 0.01 M 2,756 



The analysis of the washed and dried material showed that it con- 

 tained 68 per cent carbohydrates, 18 per cent gelatine-like material, 

 and 14 per cent of salts. It is of interest to note that these algae, which 

 inhabit the shore, display a course of acidity through the day generally 

 similar to that of other thick and succulent plants by which the acidity 

 is highest in the morning, decreasing toward the end of the day, but 

 sometimes rising before night. ^ 



The vacuolar fluid of the plant-cell may be taken to carry minute 

 quantities of the carbohydrates which enter into the protoplastic gel 

 at all times and, in addition, the sugars which figure so prominently in 

 the metabolism of the plant. The mucilage and pentosans in general 

 change but slowly and are to be considered as being of importance 

 chiefly by reason of their properties and effects as constituents of the 

 colloidal structure. The presence of sucrose and dextrose of course 

 modifies the osmotic properties of the cell, and as these substances are 



^ Clark, Lois. Acidity of marine algse. Puget Sound Marine Sta. Publ. 1, No. 22. 1917. 



