Chap, ii.] VEGETAL NUTRITION'. 91 



the radical hairs, the substances, borne on by the water which 

 holds them in solution, pass from cell to cell, each bori-owing 

 from each, in proportion as the nutritive waste goes on. In 

 plants with roots, this ascensional movement of the liquids 

 drawn from the soil is facilitated by the presence of those vessels 

 and vascular bundles we have previously described ; there arc 

 indeed no roots except in the plants whose cellular tissue is 

 traversed by vessels. In the spring the flow of the sap is so 

 abundant that it invades everything ; cells, fibres, vessels, even 

 the interstices of the cells or intercellular meatus. This flow 

 thus ascends from the root to the leaves, but circulates more 

 rapidly in the vessels, where it encounters fewer obstacles, and 

 is, in a certain measure, raised by capillarity. The grand 

 movement of ascension is accomplished through the central part, 

 through the ligneous body, or through its exterior zone, younger 

 and less incrusted if the vegetal is already agedi Very certainly 

 multiple causes, endosmosis, difEusion, capillarity, the nutritive 

 fixation of the alible matei-ials in the buds, evaporation on the 

 surface of the leaves, co-operate in the ascension of the sap ; but the 

 most powerful cause is assuredly the absorption exercised by the 

 ascensional cells of the roots. In effect a plant can live and ac- 

 tively live when its radical extremities alone are placed in water. 

 Besides this grand general movement of the sap there are 

 others more interesting perhaps, those, namely, of the contents of 

 the cell, of the protoplasm. This liquid, which we know to be 

 habitually an albuminoidal liquid, is granulous, and we see in 

 nearly all plants its granulations execute along the walls of 

 the cell or of the fibro-cell a gyratory movement. They mount 

 on one side and re-descend on the other. This protoplasmic 

 movement is a vital movement connected probably with the 

 molecular exchanges and reactions of nutrition. It is accom- 

 plished only within determinate thermometrical limits. The 

 minimum limit approaches degree, the maximum limit is from 

 46 to 47 degrees. It is toward 35 to 37 degrees that the speed 

 of the protoplasmic current attains its maximum. When it is the 



