60 



COURSE OF THE SAP. 



PT. 11. 



plum-stocks from 4 to 5 feet high, the plum-stocks 

 taper in the usual way, from below upwards ; but in 

 the course of years the growth of the peach appears to 

 overpower the stock, and it will be seen to taper from 

 above downwards. This over-growth says distinctly 

 that it comes 'from above ; but that this over-growth 

 is plum, not peach, says as distinctly that it is not 

 solely from above. I think it, then, probable that the 

 upward sap may communicate laterally throughout 

 from the wood to the bark ; and that, for the growth 

 in girthing, it may be necessary to bring together, on 

 the common ground on which the new external layer 

 of wood and the new internal layer of bark are depo- 

 sited, a sap which has been subjected to a triple elabo- 

 ration, namely, juices of the upward sap — the product 

 of chemical decomposition, assimilation, and elabora- 

 tion in the stem, and those of the downward sap — 

 which have been subjected to res]Diration, transpiration, 

 and elaboration in the leaf, and to all these processes 

 in their descent through the bark ; finally, that a 

 fourth elaboration of those saps may take place, on 

 their junction between the wood and the bark, for the 

 deposit of the new growth in girthing there. I confess 

 that this is terrible guess-work ; but I choose and state 

 the theory which appears to me to have the least 

 guess-work. As I have said throughout, all is doubt 

 and difficulty. We may at least acknowledge our 

 ignorance in the afiair. To be ignorant is bad enough ; 

 but to be ignorant of one's own ignorance is worse. If 



