UPWARD TRANSPORT OF ORGANIC MATTER 



13 



distances from the terminal bud so as to vary the amount of 

 stored food available between the ring and the growing 

 point. 



Table 1. — Effect of Ringing at Different Distances from the 



Terminal Bud upon Subsequent Growth 



Crataegus ringed Apr. 8 before bud break. Measured May 8 



Check not ringed 



Ringed in 2d internode from the tip 



^i xylem and ^i of phloem cut away in 2d internode . . 



Ringed in 4th internode from the tip 



3^ of xylem and ^i of phloem cut away in 4th internode 



Ringed at base of 1-year wood 



Ringed on 3- and 4-year wood 



Av. shoot 



elongation, 



mm. 



The effects of this ringing on the transport of food in 

 Crataegus, as indicated by growth of the bud above the ring, 

 are shown in Table 1. From these results it is apparent 

 that something carried by the phloem is necessary for shoot 

 growth. It seems probable that the lessened growth 

 cannot have been due to injury to the xylem resulting 

 from its exposure, because if three-fourths of the xylem is 

 exposed and half of it is completely severed, shoot growth 

 is practically normal. This is evident from the data in 

 Table 1. The two most obvious explanations are that the 

 xylem carries no solutes, or that it carries some but does 

 not carry all the kinds essential for growth. Since the 

 xylem is rich in carbohydrates and low in nitrogen, while 

 the phloem is especially rich in nitrogen, it would seem 

 likely that the cessation of growth above a ring was not 

 due to a deficiency of carbohydrate but to a deficiency of 

 nitrogenous material carried in the phloem. Tests for 

 starch, however, showed that at the time growth practically 

 ceased none was present in any part of the stem above the 

 ring, while starch was abundant in the storage tissues of both 

 xylem and phloem immediately below the ring. If nitrogen 



