Abstract
Increasing attention is being paid to the physico-chemical properties of plant saps. Earlier studies were devoted almost exclusively to the problems of the osmotic concentration of the plant saps, particularly as related to environmental conditions. Dixon and Atkins 1 pointed out that in order to secure uniform samples of sap the plant tissues must be made permeable by freezing. They used liquid air for freezing the material, and later Gortner and Harris 2 modified this method by using a simple salt and ice bath. Since that time a voluminous literature has accumulated 3 in regard to the influence of geographical environment and climate on the osmotic properties of plant saps. In most of the work carried out by Harris, and Harris and Gortner the electrical conductivity of the tissue fluids has been recorded, in addition to osmotic concentration, but it is only recently that a new factor has been shown to be of importance.
Newton and Gortner 4 devised a technic for the measurement of “bound water” i. e., the water which appears to be associated with hydrophilic colloids and consequently is differentiated from the free water which is free to dissolve organic and inorganic solutes. Newton 5 , 6 , 7 has demonstrated that a measurement of bound water content is of great importance in the study of winter hardiness of plants, and in similar unpublished work Newton has likewise demonstrated that measurements of bound water are of importance in studying problems of drought resistance. Robinson 8 , 9 showed bound water to be a factor in ecological problems of insects. Gortner 10 has called attention to some of the relationships involving free and bound water as affecting biological problems.
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