COURSE or FOOD DISTRIBUTION 169 



two sides of the branch are throughout its length bare of leaves; 

 and the smaller branches arise from the larger also in .two rows, 

 so that if the food descending from the leaves took a straight 

 course down the branch this would be without nourishment 

 throughout more than half of its body since the food travels 

 with difficulty out of one bundle through intervening tissues into 

 another as shown on page i6o. But this difficulty does not exist 

 in uninjured plants because the bundles are so knit together by 

 anastomoses (Figs. 20 and 49, B), that the food from one side 

 of a stem can be shunted to another side whenever there is need. 

 Likewise in Indian corn, as a rule more corn is produced on one 

 side of the stalk than on the other, but the more fruitful side has 

 taken contributions from the leaves of the opposite side through 

 the numerous anastomoses at the nodes. 



These examples will serve to illustrate the general statement 

 that whenever, or for whatever cause, one side of a plant requires 

 food that the leaves on that side are unable to furnish all other 

 sides may be drawn upon, since all the vascular bundles are 

 knit together in one system. 



The course of food distribution will now be summed up: 

 When growth begins in the spring food is carried to the un- 

 folding buds upward through the sieve tubes and tracheal tissues 

 from its place of storage in branches, trunk, and roots. Soon the 

 leaves have grown forth and begin the construction of new food. 

 This flows out of the leaf through the border parenchyma cells 

 and phloem, and on reaching the branch it takes the direction 

 compelled by the plant's need. It may flow down through the 

 phloem or up through the phloem and tracheal tissues. 



Whether the food flowing down or up shall be used at once 

 or stored for future use depends on the 'need of the plant. So 

 long as growth is rapid, and during the period of flowering and 

 fruiting large quantities of food are put to immediate use. 



As the food travels down or up through the phloem a part 

 of it is removed from these, longitudinal highways for the im- 

 mediate nutrition of the cambium and part is carried farther 

 inward by the medullary rays and used by them and other 



