97 



The plant seems to get on better if the sieve-tubes be left 

 untouched in the experiments of ringing trees, than it does if 

 they are removed along with the other elements included by 

 the ring. 



In some plants also, as the Euphorbias, the Poppies, and the 

 section of the Composite represented by the Dandelion, we 

 find certain vessels present in the bast, known as laticiferous 

 vessels, containing a milky fluid, one of the constituents of 

 which is proteid material which is thus transported in this 

 channel from one part of the plant to another. These vessels 

 seem to have some influence in distributing the substances 

 formed in the leaves ; their use for this purpose is, however, a 

 secondary one, and they are not essential elements, since they 

 are only present in a few plants. 



Lastly, we have the movement of water in the process of 

 growth. 



The growth of the cells of plants is always connected with 

 the absorption of water, and this not only as regards the size of 

 the cell vacuole ; for the growth of the cell-wall, &c, is also 

 accompanied by the intercalation of particles of water between 

 the solid micellae. 



Water must, therefore, be conducted to the growing cells and 

 tissues, and when the organs which absorb the water lie at a 

 distance from those which require it from their growth, the 

 movement of liquid is necessarily considerable. 



Water is also required by the organs of assimilation, since it 

 gives the hydrogen required for organic compounds. 



The reservoirs of nutrient matter, in which substances such 

 as starch are for a time accumulated, also require water to enable 

 them to dissolve these substances, in order that they may be 

 transported as formative material to the leaves and growing 

 apices of roots and stems. All these movements of water, which 

 are necessarily connected with nutrition and growth, proceed 

 slowly, like growth itself. Their direction is from the nearer 

 parts first, then from the more distant, and finally from the 

 external medium. The water travels slowly by osmosis, from 

 cell to cell, through the parenchyma, and as the equilibrium 



