CONSUMPTION OF CARBOHYDRATES DURING STARVATION. 73 



The course of the depletion of the stored carbohydrates can be seen in 

 table 37. The proportion of the various sugars maintains a surprising 

 regularity as the depletion proceeds. This is an important fact in view of 

 the opinion which has been frequently expressed regarding the physiological 

 role of the pentoses. These sugars have been considered by some plant 

 physiologists as end or waste products of the normal metabolism, which 

 accumulate as the plant becomes older. Were this the case it would be 

 expected that, in plants subjected to conditions such as these, there would be 

 an increase in pentoses, at least relative to the other sugars. But this is 

 found not to be the case ; the pentoses apparently are drawn into the course 

 of carbohydrate metabolism to a marked degree. The starch, which is 

 present in very numerous minute grains, disappears slowly. After 72 days 

 there are visible but a few scattered grains; and after 92 days practically 

 all of the starch has disappeared. 



TABLE 37. Carbohydrate-content of Opuntia phwacantha during starvation. 



in percentages of the dry material. 



Values 



Another experiment was undertaken to determine the effect of starvation 

 on the subsequent photosynthetic activity as well as of feeding with cane- 

 sugar and dextrose. A number of joints of Opuntia phceacantha were left 

 in the dark at 28, as previously described, for 189 days. One set of joints 

 (A) was then analyzed to determine the status of the carbohydrates. The 

 remaining joints were placed in battery jars containing water, in such a 

 manner that the cut end was just below the surface of the water. Within 

 10 days all the joints had produced roots 2 to 5 cm. in length. The plants 

 were then divided into 3 lots of 7 joints each and treated in various ways. 

 B was placed with the roots in a sterile 1 per cent cane-sugar solution ; C 

 with roots in a sterile 1 per cent dextrose solution, both in the dark at 28 ; 

 and D with the roots in a nutrient solution, in the sunlight. The plants 

 remained thus for 60 days ; the solutions were changed frequently. At the 

 end of this time the plants were all in a very healthy condition and were 

 analyzed in the usual manner; the results are given in table 38. 



