Imbibition and Growth of Opuntia. 



131 



the condition of the fresh material. It is important that the thick- 

 ness of the slices before drying be approximately equivalent. 



The measurements obtained from living sections inclusive of the 

 entire thickness of joints and from dried slices, given in table 103, 

 illustrate the seasonal variations in mature stems. 



TABLE 103. Swelling of mature joints at different seasons. 



The continued dry condition is seen to result in desiccation, which, 

 of course, is followed by increased hydration when such living sections 

 are swelled, the maximum effect being reached in January, before the 

 beginning of the winter rains. 



The tests of the dried sections which show the swelling after the 

 colloids have been subjected to the action of concentrating salts have 

 a value derived from the fact that all are reduced to an equivalent 

 water-content, accompanied by irreversible coagulations of the more 

 complex proteins. Although we here introduce a new set of conditions, 

 the effects of which are not easily to be evaluated, yet it is none the 

 less significant that the entire series of preparations reach their 

 maximum water capacity at the end of March. Since some changes 

 may have been brought about in the proteins, it is important to 

 follow the course of the carbohydrates. 



The variation in the sugar-content is best illustrated by the data 

 given in table 104, as determined by Dr. Spoehr. 1 



It is clear that the colloidal material of the cell-mass of this plant 

 does not come to a condition of highest imbibition capacity at the end 

 of the period of desiccation in the season of low temperature, but the 

 maximum is found after the beginning of a season of rising temperatures 

 and of accumulating sugars, coupled with an inadequate water-supply. 



1 Spoehr, H. A. The pentose sugars in plant metabolism. The Plant World, 121 : 365-379. 1917. 



