226 VEGETABLE PHYSIOLOGY 



To a certain extent the cortex of the plant shares the 

 translocatory function. The contents of its cells include a 

 certain amount of carbohydrate material, but their reaction 

 is distinctly acid, so that this region is probably concerned 

 much more definitely with the transport of vegetable acids, 

 so far as it takes part in translocation at all. At the same 

 time it is impossible to localise the transport of food 

 exclusively in the bast. 



Other parenchymatous tissues are sometimes the region 

 of transport. In many germinating seeds there is a trans- 

 ference of large quantities of nutritive substance across the 

 endosperm to the embryo, and in young seedlings similar 

 transport takes place through pith as well as cortex. 



The vessels of the wood, which we have seen are the paths 

 of the transpiration current are probably not concerned 

 normally in the translocation of manufactured products, 

 though exceptionally they may contain certain amounts 

 of proteins, amido-acids, &c., in solution. Their function 

 in this respect is, however, unimportant, and the presence 

 of such bodies in them is mainly accidental. 



An important exception is seen in the resumption of the 

 growth of a tree in the spring. Before the unfolding of its 

 leaves enables photosynthesis to commence, a stream of food 

 from the winter reservoirs takes place which travels upwards 

 in the wood. 



It is doubtful how far the laticiferous systems, which 

 are present in many plants, may be regarded as channels 

 for translocation. No doubt latex contains many nutritive 

 products, both nitrogenous and non-nitrogenous, but there 

 is reason to think they are to be referred to the storage 

 rather than to the transporting system. 



