MECHANISMS FOU OOXVEVAN'CE TO AXO FRO. 



479 



a store of materials, so that they may be nourished until they cjin manufacture 

 for themselves the necessary food from the air, water, and soil. The places whoi-e 

 spores and seeds are produced, tliorcfore, constitute an important destination for 

 certain journeying materials. Finally, it al.so happens that in regions where a 

 temporary standstill of the vital activity of the plants occurs, and where the 

 succulent green foliage is liable to be dried up by the periodic drought, or frozen 

 by the winter cold, all the useful substances are withdrawn from the threatened 



Fig. 129.— Leafless Branches of Tccoma radicans, rooted on a wall. 



leaves, and are deposited in a suitable foi-m in safe places, and stored uj) for 

 emploj-ment later. In these instances, these safe places, these storehouses or 

 reservoirs, form the destination of the transported materials. 



Not only are there channels of distribution to the various destinations 

 enumerated, but we find even distinct routes provided for the different substances 

 transmitted. Investigations have shown that the conducting mechanisms divide 

 the work to some extent between them. Tlie medullary rays and wood paren- 

 chyma chiefly conduct carbohydrates, the former radially, and the latter longitudi- 

 nally, in the stem. The vascular bundle sheaths of the leaf-veins are particularly 

 rich in glucosides. Certain tracts of cells in the parenchyma accompanying the 

 vascular bundles in the stem also conduct glucosides, while others conduct sugars 



