56 CARNEGIE INSTITUTION OF WASHINGTON. 



The subject has been mistakenly dealt with as a unified process, or 

 as a series of successive reactions in studies of temperature effects, with 

 the result that the student now has available coefficients of doubtful 

 value within not more than a third of the range of ordinary plants. 



The chief defect in all three groups of research consists in the neg- 

 lect of the fact that the metabolism upon which growth depends is 

 a constellation, not a linear series of transformations, and that the 

 most important part of the process lies within the realm of surface 

 tensions in which the play of imbibition is the determining feature. 



A further prerequisite to rational advance in researches on growth 

 is a recognition of the fact that a general identity of protoplasm of 

 plants and animals does not exist. The relative amounts of proteins, 

 carbohydrates, hpins, and salts in two groups differ widely. In addi- 

 tion to the capacity of the plant to synthetize carbohydrates, amino- 

 acids, etc., which the animal can not, the respiration and metabolism 

 of the plant are predominantly carbohydrate, while those of the animal 

 are proteinaceous. 



The fundamental and ultimate structure or architecture of proto- 

 plasm is a result of the force of surface tension and is a gel in which 

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

 In the more liquid phase the molecules of 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 architecture which has been likened to 

 that of a mesh, felt, foam, or honeycomb in which the denser phase 

 forms the framework and the fluid fills the interstices. Under certain 

 conditions the phases may be reversed and the solid particles may be 

 rounded into globules entirely surrounded by the fluid. 



The essential feature of an idealized growth is the accretion or addi- 

 tion of water and material to the mass of colloid constituting the 

 cell. The actual mechanism of incorporation is not easily deline- 

 ated. The end-process is one, however, of hydration of a colloid, and 

 it is upon this process that interest naturally centers in all studies 

 of growth. The manner in which this takes place is one which may 

 be most aptly designated as molecular imbibition, although it is not 

 so simple as to be adequately and inclusively described by any single 

 term. It is considered by some writers to be primarily absorption 

 in which the entering liquid passes between the fibers of the spongy 

 structure or honeycomb plates of the protoplastic gel as it would into 

 a layer of fine lamellae or a dense tangle of closely piled fibers. 



In that type of growth in which carbohydrates or proteins are car- 

 ried into the mass by water, it may be seen that the accumulation 

 of the additional material in the more liquid phase would, by the 

 action of surface tension, result in the aggregation of new masses of 

 material. Such formation of additional elastic gel structure might 



