HOW STOCK AND SCION UNITE. 



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lower parts of a plant must b^ gradually encased in solid matter 

 derived from branches, and that consequently, of necessity, the 

 stock of a plant must be enveloped iu layer above layer of the 

 wood of the scion. It is needless to repeat the arguments 

 employed in support of this view ; they were cogent, and for a 

 long time held to be irrefragable. The application of the theory 

 to graftrag led, among other things, to the conclusion that if a 

 scion would take it would speedily form a sheath of wood over 

 the stock, and thus secure itself for ever. Once, to form a good 

 union was, therefore, looked upon as sufficient security for the 

 permanent life of the grafted plant. It is true that cases, 

 apparently at variance with the theory, occurred 

 every now and then, but plausible explanations 

 of such instances were readily found. 



It is, however, now certain that although 

 wood is formed by a descending process, yet 

 that its descent is not in an organized state. 

 Fluid matter, out of which it is produced, 

 passes, indeed, from above downwards, but the 

 formation itself is wholly local and superficial, 

 and consequently there is no such thing as an 

 encasement of the lower part of a tree by . 

 wood descending from above. That important 

 fact having been once established, the union 

 of a scion and its stock evidently becomes a 

 case of mere adhesion, extremely powerful in 

 some cases, feeble and readily destroyed in 

 others. There are, therefore, two essentially 

 different results obtained by grafting — the one 

 permanent, the other transitory. The follow- 

 ing example affords a new demonstration that 

 the union between a scion and its stock is no 

 other than that now described. (Fig. LXV.) 



About the beginning of September, 1853, 

 Dr. Allan Maclean, of Colchester, an ingenious 

 experimentahst and good physiologist, grafted a young plant 

 of the White SHesian Beet upon a root of Eed Beet, and 

 vice versa. At the time of the experiment the plants were 



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0J. 



Ill 



Pig. LXV. 



