MACDOUGAL AND SPOEHR— GROWTH AXD IMBIBITION. 335 



protein synthesis and catabolism as is probably the case in animals. 

 In fact these plants behave largely like masses of gel of carbohydrate 

 nature. 



Roughly the fresh material of the growing and mature joints is 

 composed of about : 



Per Cent. Per Cent. 



Water 95 75 



Crude protein 0.5 i.o 



Carbohj-drates hj-drob-zable with i.o per cent. HC! 5.0 lo.o 



Cellulose 1.0 3.0 



Crude fat 0.25 0.5 



Ash 1.0 3.5 



The total carbohydrate content and of food supply in general 

 is of little significance or value in studying the various functions of 

 an organism such as the cactus. It is rather the nature of the 

 sugars, or the degree of general chemical inversion, that determines 

 the supply of building material necessary for growth. The records 

 show many instances of large food supply, and all known external 

 conditions favorable for growth, and still no such action taking 

 place. The question of rest period undoubtedly is largely one of 

 adjustment of chemical inversion and reversion, and in general the 

 conditions favoring the awakening of buds are those in which in- 

 version has attained a lead over reversion, permitting a sufficient 

 accumulation of plastic material ; while on the other hand, an ac- 

 cumulation in the protoplasmic medium of the products of rever- 

 sion aftects the inhibiting of growth. It seems therefore that in 

 order for growth to occur there must be a sufficient supply of the 

 simpler sugars necessary for respiration as well as for the synthesis 

 of new substances, that synthesis can overbalance the break-down 

 with the accumulation of new material, the latter being the product 

 of an irreversible reaction. In the study of the relation of carbo- 

 hydrates to growth it is therefore a question of the carbohydrate 

 balance, the ratio of the simple to the condensed sugars that is of 

 prime iinportance. 



The problem of determining the different sugars in a growing 

 organism is one of great difficulty because, as has been indicated, of 

 the large number of sugars belonging to the same group and of the 

 similarity of their chemical properties. It must therefore suffice to 



