Constituents of Biocolloids Affecting Hydration and Growth. 29 



dissolved in the fluids which are imbibed by the gels, their probable 

 influence is a matter of some importance. An examination of the 

 effects of sucrose and dextrose on agar and gelatine and mixtures 

 of these two substances was made by Dr. E. E. Free at the Coastal 

 Laboratory, Carmel, California, in September 1916, and his results 

 show no certain effect upon the hydration of gelatine, agar, and of 

 mixtures of the two substances from water solutions containing as much 

 as 25 per cent of sucrose or dextrose. 1 More recently, E. A. and H. T. 

 Graham have found that glucose, saccharose, and lactose, when added 

 to gelatine, retard the diffusion of such acids as hydrochloric, nitric, 

 sulphuric, phosphoric, lactic, formic, acetic, and butyric, with an accom- 

 panying effect on the swelling. Diffusion was also found to be retarded 

 by sodium chloride. 2 The universal presence of both sugars and salts 

 in the plant cell gives great importance to the relations indicated. 



Mucilages or pentosans are present in varying proportions in all 

 plant cells, and it is the character and relative amounts of such com- 

 pounds that largely determine the hydration reactions of the proto- 

 plast. Of these substances agar was used most generally throughout 

 the experiments, because it goes into the disperse condition very slowly 

 and in this particular is identical with protoplasmic gels. 



According to information furnished by Mr. H. Nakano, of the Botan- 

 ical Garden of Tokyo, agar is prepared chiefly from the algae Gelidium 

 amansii Lamour, G. pacificum Okam, G. linoides Kiitz, Pterocladia 

 capillacea Born, et Thur., while some material of Gelidium subcostatum 

 Kiitz, Ceramium boydenii Gepp., Campylcephora hypenaloides Y. Ag., 

 Acanthopeltis japonica Okam, etc., may be included. The process 

 includes washing in fresh water, decoloration in the sun, milling, boil- 

 ing, filtering, maceration in sulphuric or acetic acid, freezing, and 

 drying. Modernized methods simplify this treatment somewhat. 

 Salts and nitrogen are present in the final product in minute quan- 

 tities insufficient to affect hydration. 3 



Other gums and mucilages of this group which were tested included 

 gum arabic or acacia, cherry gum, prosopis gum, tragacanth, and 

 opuntia mucilage, all of which are more readily dispersible in water, 

 but which do not go wholly into suspension even in prolonged im- 

 mersion. The mucilages of the cacti are pentosans, or substances 

 which yield hexose and pentose sugars on hydrolysis with dilute acids. 

 Substances of a similar character formed by the condensation from 

 simpler sugars may be taken to be universally present in plant cells, 

 being aggregated in the plasmatic mesh, in which condition the muci- 



1 Free, E. E. Note on the swelling of gelatine and agar gels in solutions of sucrose and dextrose . 



Science, 46 : 142. 1917. 



2 Graham, E. A. and H. T. Retardation by sugars by diffusion of acids in gels. Jour. Amer. 



Chem. Soc. 40 : 1900. 1918. 



3 For further information concerning the origin and preparation of similar products, see 



Swartz, M. D. Nutrition investigations on the carbohydrates of lichens, algae, and re- 

 lated substances. Trans. Conn. Acad. of Arts and Sciences, 16:247-382. Apr. 1911. 



