MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 343 



had a similar effect on the mixtures low in gelatine in which it was 

 tried. Its eft'ect on mixtures containing a large proportion of gela- 

 tine was not determined. The appreciable eft'ects are probably due 

 to the tying up of molecules of water analogous to the osmotic action 

 of such solutions. 



Sugar solutions of a concentration of 25 per cent, or higher are 

 not characteristic of growing regions and probably occur only in 

 storage tracts, seeds or cotyledons. While the effect would be to 

 lessen imbibition by the colloidal mass of the protoplast it is to be 

 recalled that a vacuolar fluid of such concentrations would have 

 high osmotic properties and the expansion by turgidity might mask 

 or exceed that due to imbibitional swelling. If sugars contribute 

 directly to the growth expansion of the cell it would therefore be in 

 the later stages of development and by osmotic action. 



A duplicate series of tests of the behavior of an admixture of 

 starch with agar gave the following results : 



Swelling. 

 Agar go — Starch jo. 



Water. HCl N/ioo. NaOH N loo. 



1275 per cent. 541-6 per cent. 496.6 per cent. 



The complication of the carbohydrate gel by the addition of starch 

 made no essential departure from the behavior of agar alone in 

 water, acidified and alkaline solutions. 



The combination of agar and gelatine gave a gel in which two 

 of the three main groups of constituents of living matter were 

 represented. 



It is not certain, however, that the combination of amino-acids 

 in gelatine is duplicated in the plant and it was deemed important 

 to test the effects of simpler amino-acid compounds and of the 

 more complex albumens on the swelling of agar, as representing the 

 basically important carbohydrates. Solutions of the various mix- 

 tures were poured on glass plates in layers about a centimeter thick 

 and 3 by 5 cm. in area. Desiccation resulted in a reduction of the 

 length and width to about half of the original. The thickness how- 

 ever was reduced to one-tenth or even as much as to one-thirtieth of 

 the original, and having a thickness of .1 mm. to .3 mm. in most 



