26 EXPERIMENT STATION RECORD. [Vol. 41 



process lies within tlie realm of surface tensions in which the play of imbibition 

 is the determining factor. 



A further prerequisite to rational advance in researches on growth is a recog- 

 nition of the fact that a general identity of protoplasm of plants and animals 

 does not exist. The relative amounts of proteins, carbohydrates, lipins. ami 

 salts differ widely l)etween these two groups. While the plant can synthesizi' 

 carbohydrates, amino acids, etc., which the animal can not, the respiration and 

 metabolism of the plant are predominantly carbohydrate, while those of th(> 

 animal are proteinaceous. It is held that the fundamental and ultimate struc- 

 ture of protoplasm is a result of the force of surface tension, and is that of a 

 gel in which the solid material occurs in two main states or phases with water. 

 In the more liquid phase the molecules «f the substance are associated with such 

 a large proportion of water as to be in a liquid condition, while in the more solid 

 phase the proportion of water is much less. These phases have a distinct archi- 

 tecture likened to that of a mesh, felt, foam, or honeycomb in which the denser 

 phase forms the frameworlc and the fluid fills the interstices. Under certain 

 conditions the pha.ses may be reversed and the solid particles may be rounded 

 into globules entirely surrounded by the fluid. 



The essential feature of an idealized growth according to the present con- 

 ception is the accretion or addition of water and material to the mass of colloid 

 constituting the cell, the end-process being the hydration of a colloid. In that 

 type of growth in which carbohydrates or proteins are carried into the mass by 

 water, such an accumulation would, under surface tension, result in the aggre- 

 gation of new masses of material. Such formation of additional elastic gel 

 structure might occur throughout the entire cell, but in actuality would be modi- 

 fied and controlled at every point by the factors which affect hydration. 



The nature and course of growth in higher plants, D. T. MacDougal {Car- 

 negie Inst. Washinyton Year Book, It (1918), pp. 58, 59.) — The results obtained 

 following the development and employment of the auxograph are said to have 

 shown that much of the present confusion as to the main features of growth 

 has resulted from attempts to compare and harmonize growth in organisms 

 presenting physical conditions not really comparable. Data obtained from 

 growth measurements on plants mentioned have shown a decrease in growth 

 rate with daily variations (swellings and shrinkage) corresponding to internal 

 changes. Shrinkage becomes more marked as maturity approaches. While 

 some portions may show continuous enlargement, older parts of the stem may 

 take up and give off water in a manner entirely reversible, showing a very wide 

 range of alterations. The estimation of the balance between water loss and 

 water supply, as implied in the experimental results here referred to, is con- 

 sidered to have given a new and more important meaning to relative humidity 

 as affecting plant growth. 



The growth mechanism of protoplasm, D. T. MacDougal (Carnegie Inst. 

 Washington Year Book, 17 (IHIS), pp. 57, 58). — Experimental studies are said 

 to have established the view that protoplasm in plants consists of a compara- 

 tively inert base of pentosans, which may be diffused or transformed only at a 

 very slow rate, in colloidal combination with proteins, amino acids; lipins, and 

 salts to form a complex mass varying from the liquid condition to that of an 

 elastic gel. The volume and changes in volume constituting growth are deter- 

 mined by the proportion of water taken up, this in its turn being a resultant of 

 the proportions of the main constituents. Other soluble carbohydrates probably 

 do not affect directly enlargement of the protoplasmic mass, but they may exert 

 in the vacuoles an osmotic effect additive to that of the amino acids which may 

 accumulate in these cavities. 



