DEPARTMENT OF BOTANICAL RESEARCH. 67 



tion was measured off, 50 c.c. being allotted for acidity determinations 

 (see results above), and 180 c.c. was used for determination of the 

 solid matter present. It was found that this amounted to 0.28 gram 

 for the 240 c.c. of juice obtained from sections having a total volume 

 of 40 c.c. when fresh. The actual solid matter of the sections, including 

 the cell- walls, may be taken as 10 per cent of the whole, or as 4 grams. 

 Of this, 7 per cent was dissolved out in water. The extraction of this 

 amount of material could readily be held to account fully for the 

 changes which take place in hj^dration and which give different expan- 

 sions in the second immersion. 



It is quite clear that no explanation of absorption of solutions by 

 cell-masses or of plasmolysis may be adequate or greatly useful which 

 does not take into account certain fundamental mechanical features of 

 the cell-structure. Among these are to be included the phase boun- 

 daries of the colloids of the cell-wall, of the vacuoles, of the proto- 

 plast, and of the multiple and varying structures in the protoplasm. 



Plasmolysis by osmotic action is accompanied by losses and by 

 penetrations and perfusions of complex character in the many phases 

 of the cell colloids. Plasmolysis in wilting is in some respects a simpler 

 matter. Vaporization of water from the cell-walls is followed by 

 replacement movements from the cell colloids, which result first in a 

 lessened volume of the protoplast and finally in the progressive con- 

 centration of all substances, especially those dissolved in the vacuoles, 

 and in the more liquid phases of the colloids. The fact that the acids 

 may be readily extracted in greater proportion from dried specimens 

 than from fresh tissues suggests that these substances may have crys- 

 tallized out to some extent after the manner of amino-acids incorpo- 

 rated in colloidal mixtures. The same may be true to some extent of 

 the salts. There is also much in favor of the conclusion that changes 

 take place in the colloidal mesh, as a result of a loss of water and of the 

 action of adsorbed bases which cause coagulations not reversible by 

 simple hydration. 



Measurement of Growth in Terms of Volume, by D. T. MacDougal. 



Measurement of growth in the higher plants usually denote the rate 

 of increase of stems, roots, etc., in which the variation in length or 

 thickness is taken without reference to the volume of the enlarging 

 cell-masses. The growing joints of Opuntia offer some features for 

 more exact computations, but the rounded or globular fruits offer the 

 best material for a consideration of the actual and relative accretions 

 to the enlarging organs. 



The usual method of expression of increase in a tomato would be in 

 terms of varying diameter, but the actual increase is to be calculated 

 from the formula V = 4/3 PiR^—4/S Pir^, in which r = the radius at the 

 beginning of the measurement and R = the increased diameter, the 



