1040 



takiB place through a very different system of parts, the descent of the 

 elaborated sap being limited to one direction and confined only to 

 one part of a plant, whilst the crude sap, in addition to its passage 

 upwards, is diffused throughout its entire substance. Now, there is 

 no other system of organs in plants, excepting vessels, which are ca- 

 pable of thus limiting the passage of the elaborated sap ; nor is there 

 any one but the intercellular tissue (that is, the tissue filling up the 

 intervals between the cavities of the cells) which can allow the crude 

 sap to have such an universal diffusion. 



" 48. Now, as long as the process of elaboration is going on most 

 actively in the leaves and other foliaceous organs, and the material 

 elaborated is disposed of in the parts which are situated below them, 

 that is, nearer the roots, the direction taken by the elaborated sap 

 along the vessels must be downwards, and thus it ought to continue 

 until these organs have accomplished all the purposes for which they 

 were intended, until, after having completed their own development, 

 they have provided for the propagation of the species by the produc- 

 tion of seed. In this case the process of elaboration is first employed 

 in forming cells, and afterwards in depositing within them solid mat- 

 ter for the nutrition of the germs at some future period. As the pro- 

 cess of deposition advances, the conditions become less and less 

 favourable for endosmose, and after the cells have become full, these 

 conditions cease to exist, and no more fluid is attracted into the in- 

 tercellular tissue surrounding them : that which they did contain eva- 

 porates, and the seed, as well as those parts whose function had been 

 subservient to its growth and maturation, become so altered in their 

 physical characters as to unfit them for being retained any longer on 

 the plant, until also a provision has been made for the leaf-buds of 

 the ensuing year, by a deposition of starch or some similar substance 

 in the vessels and cells of the stems and roots. Hence, if the root of 

 a vine be dug up in the winter, the cells and vessels situated in the 

 outer layer of wood are found filled with starch granules ; if in the 

 spring, after it has ceased bleeding, as it is termed, and the leaves 

 have appeared, the quantity of starch in these vessels and cells will 

 have very much diminished, and at a still later period it will be found 

 almost to have disappeared ; and lastly, until a deposit has been 

 formed of finely granular matter around the last year's wood. This 

 deposit is contained in minute square cells, compressed in the direc- 

 tion of a line extending from the centre to the circumference of the 

 stem, and forming collectively a dark-coloured ring all around the 

 last year's layer of wood, by which a thin transverse section made in 



