MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 351 



4 P.M. Whether complete neutrahzation or alkahne conditions 

 ever occur naturally in this plant is doubtful. 



The notable augmentation of imbibition which accompanies 

 complete destruction of the balance of acid in the shoot of Opuntia 

 under experimental conditions has already been described on p. 295. 

 It has also been found that the mid-afternoon checking of growth 

 characteristic of shoots of Opuntia which have accomplished a 

 fourth or a third of their development, did not appear in the single 

 bud, the development of which from a starved joint has been fol- 

 lowed since the section of this paper dealing with growth was 

 written. 



The almost rhythmic undulations of the auxographic tracing of 

 the elongation of a wheat leaf corroborated by measurements with 

 the horizontal microscope suggest that growth in this organ may be 

 accompanied by metabolic processes by which the balance of acidity 

 and alkalinity falls now on this and then on that side, there being 

 of course periods in which the growing protoplasts or some of them 

 were in a neutralized state. During this time of course imbibition 

 might be four to eight times as great as in either acid or alkaline 

 conditions. 



The change from any one of these conditions is of course accom- 

 panied by variations in imbibition. The character of the change is 

 readily recognizable in the swelling of colloids, and it is believed 

 that similar interpretations of the auxographic record of growing 

 organs will be possible. The colloidal sections used for experimenta- 

 tion have a general identity with cell-masses except as to the lipin 

 constituents. The part which these substances might play in the 

 mechanics of growth can not as yet be made the subject of profitable 

 conjecture. The analogies as to the action of the salts to be found 

 in plants are also yet to be determined, and probably involve some 

 of the phenomena studied as " antagonisms." 



The striking similarities in behavior between the pseudo-proto- 

 plastic material and cell-masses makes possible some new correla- 

 tions in metabolism, imbibition and growth. It is hardly necessary 

 to add in conclusion that whatever measure be given the contribu- 

 tions embodied in the present paper, the results presented do not 



