i66 



TRANSPORT OF FOODS 



When the food reaches the branch which bears the leaf it 

 may pass through the phloem down or up, or part may pass 

 down and part up at any given moment. Some of the food 

 may also be transferred to the water tubes in which it will be 

 hurried along to the growing apex of the branch or to fruits 

 and seeds in course of formation, and be put to immediate 

 use (Fig. 92). When the branches are still growing in length, or 

 when fruit is developing, a great deal of the food goes up to 

 nourish the new growth. After growth in length has ceased, 



upwar 



Tracheal tube carrying food upward 

 from the leaves 



Fig. 92. — Diagram illustrating the descent of food from the leaf into the stem, and its 

 circulation upward and downward through the sieve tubes, and upward through the 

 tracheal tissues. 



and if fruit is not forming, doubtless most of the food goes down- 

 ward to sustain the cambium in its production of new tissues, or 

 for storage until demand is made for it at the time of flowering 

 and fruiting in annuals, or when growth is resumed in the spring 

 in the case of perennials and biennials. 



In Indian corn, for instance, after blossoming, the food is 

 for the most part sent into the ears, and that which is made 

 by the lower leaves passes up, and that by the upper leaves 

 down, to the ears for storage in the form of starch, proteids, and 

 oils (Fig. 93). 



In perennial plants, such as trees, part of the food made in 

 spring and early summer is used at once in growth in length and 



