.^f70 scions.; 



332. For mis reason pure silex, in which no stimulating 

 substances are contained ^silver sand), is the best adapted for 

 promoting the rooting of cuttings that strike with difficulty. 



333. And for the same reason, cuttings with what gardeners 

 call a heel to them, or a piece of the older wood, strike root 

 more readily than such as are not so protected. The greater 

 ageof the tissue of the heel renders it less absorbent than tissue 

 that is altogether newly formed. 



334. It is to avoid the bad effect of evaporation that leaves 

 are usually for the most part removed from a cutting, when it 

 is first prepared. 



XIV. Scioss. 



335. A scion is a cutting (311.) which is caused to grow 

 upon another plant, and not in earth. 



336. Scions are of two sorts, scions properly so called, and 

 buds. (354) . 



337. Whatever is true of cuttings is true also of scions, all 

 circumstances being equal. 



338. When a scion is adapted to another plant, it attracts 

 fluid from it for the nourishment of its leaf buds until they can 

 feed themselves. * . ■ 



339. Its leaf-buds thus fed gradually grow upwards into 

 branches, and send woody matter down wards, which is analo- 

 gous to roots. 



340. At the same time the cellular substance of the scion and 

 its stock adheres (19 ) so as to form a complete organic union. 



341. The woody matter descending from the bud passes 

 through the cellular substance into the stock, where it occupies 

 the same situation as would have been occupied by woody 

 matter supplied by buds belonging to the stock itself. 



342. Once united, the scion covers the wood of the stock 

 with new wood, and causes the production of new roots. 



343. But the character of the the woody matter sent down 

 by the scion over the wood of the stock being determined by 

 the cellular substance, which has exclusively a horizontal 

 developement (73.), it follows that the wood ot the stock will 

 always remain apparently the same, although it is furnished 

 by the scion. 



344 Some scions will grow upon a stock without being able 

 to transmit any woody matter into it ; as some Cacti. 



345. When this happens, the adhesion of the two takes 

 place by the cellular substance only, and the union is so 

 imperfect that a slight degree of violence suffices to dissever 



346 And in such cases the buds are fed by their woody 

 matter, which absorbs the ascending sap from the stock at the 

 point where the adhesion has occurred ; and the latter, never 

 augmenting in diameter, is finally overgrown by the scion. 



