SCIONS. 139 



330. If ripened cuttings are upon the whole the most fitted for multi- 

 plication, it is because their tissue is less absorbent tlian when youufier, and 

 that they are less likely to suffer eitlier from repletion or evaporation. 



331. For, to gorj,'e tissue with food, before leaves are in action to decom- 

 pose and assimilate it, is as prejudicial as to empty tissue by the action of 

 leaves, before spongioles are prepared to replenish it. 



332. For this reason, pure silex, in which no stimulating substances are 

 contained (silver sand), is tlie best adapted for promoting the rooting of 

 cuttings that strike with difliculty. 



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 age of 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. Scions. 



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

 plant, and not in the earth. 



336. Scions are of two sorts : scions properly so called, and bttds (354). 



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

 stances being equal. 



33S. 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 upward into branches, and 

 send woody matter downward, which is analagous 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 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 of 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 trans- 

 mit any woody matter into it ; as some Cacti. 



345. W^hen 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 sntlices to dissever them. 



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 over- 

 grown by the scion. 



347. When, in such instances, the communication between the stock 



