MacDOUGAL— HYDRATION AND GROWTH. 347 



well as in the protoplast, must be considered as simply mixed in an 

 intimate manner in interlocking meshworks, foams or whatever 

 interpretations may be given to the structures revealed by cytological 

 technique. Living matter made up in this manner may be miscible, 

 or immiscible, according to the nature of the pentosan or protein en- 

 tering into its composition. It is obvious that the protoplasm in 

 which the carbohydrate element is like agar would not be " soluble," 

 while a mixture composed largely of gum arable would go readily 

 into suspension. Hydration as used in this paper denotes the union 

 of water with the molecules or aggregate of molecules of substances 

 in a colloidal condition inclusive of the action by which first definite 

 proportions are taken up in so-called chemical combination, and 

 also of the indefinite absorption combinations. 



Growth may be defined as consisting chiefly in the hydration of 

 colloidal material in a living condition generally accompanied by 

 accretions to the main components as described above, although not 

 actually necessary for the conception as the ground or fundamental 

 structure of protoplasm might be increased by rearrangements of 

 material already included. The later stages of increase in volume 

 of a protoplast are coincident with the formation of denser per- 

 manent structures having the eft'ect of increasing the relative dry 

 weight with age or approaching maturity, a procedure which may 

 be taken to be universal in the tissues of the higher animals, ac- 

 cording to the researches of Donaldson, Hatai and others. 



This too is currently assumed to be the case in the tissues and 

 organs of the higher plants, but my own results include a type of 

 growth in which this is not the case. Succulents of all kinds produce 

 stems or leaves in which the percentage of dry weight of small young 

 organs such as the joints of cacti, leaves of Mesembryanthemum, 

 and fruits of the melon or berry type, is greater than that of mature 

 organs or members exemplifying a category of growth especially 

 interesting in the present connection. Succulence is due to the 

 hypertrophy or exaggerated growth of cells in which the hexoses 

 have been converted into pentosans, initially as a result of low water 

 contents of the cells, the pentosans having a high capacity for water 

 which is exerted during the remainder of the life of the cell, and it 

 is in such organs that the relative dry weight does not increase with 

 age. 



