REPORT ON THE PHILOSOPHY OF BOTANY. 39 



lateral extension, the diameter of each will remain the same ; 

 but if one grows more rapidly than the other, the diameters 

 will necessarily be different : where the scion has a horizontal 

 system that develops more rapidly than that of the stock, the 

 latter will be the smaller, and vice versd. It ia^ however, to be 

 observed, that in these cases plants are altogether in a morbid 

 state, and will not live for any considerable time. 



Those who object to the theory of wood being generated by 

 the action of leaves, either suppose — 1st, that liber is developed 

 by alburnum, and wood by liber ; or, 2ndly, that " the woody and 

 cortical layers originate laterally from the cambium furnished 

 by preexisting layers, and nourished by the descending sap *." 

 The first of these opinions appears to be that of M. Turpinf , 

 as far as can be collected from a long memoir upon the grafting 

 of plants and animals ; but I must fairly confess that I am not 

 sure I have rightly understood his meaning, so much are his 

 facts mixed up with gratuitous hypothesis and obscure specu- 

 lations upon the action of what he calls globuline. The second 

 is the opinion commonly entertained in France, and adopted 

 by M. De Candolle in his latest published work. 



The objections to the views of M. Turpin need hardly be 

 stated in a Report like this, where conciseness is so much an 

 object. Those which especially bear upon the view taken by 

 M. De Candolle are, that his theory is not applicable to all 

 parts of the vegetable kingdom, but to exogenous plants only; 

 that it is inconceivable how the highly organized parallel tubes 

 of the wood, which can be traced anatomically from the leaves, 

 and which are formed with great rapidity, can be a lateral de- 

 posit from the liber and alburnum ; that they are manifestly 

 formed long before it can be supposed that the leaves have 

 commenced their office of elaborating the descending sap ; and, 

 finally, that endogenous and cryptogamic plants, in which there 

 is no secretion of cambium, nevertheless have wood. 



Such is the state of this subject at the time I am writing. To 

 use the words of M. De Candolle, " The whole question may 

 be reduced to this, — Either there descend from the top of a tree 

 the rudiments of fibres, which are nourished and developed by 

 the juices springing laterally from the body of wood and bark, 

 or new layers are developed by preexisting layers, which are 

 nourished by the descending juices formed in the leaves J." 



As this is one of the most curious points remaining to be 

 settled among botanists, and as it is still as much open to dis- 



* De Candolle, Physiologie Vegelale, p. 165. 



t See Annales des Sciences, vols. xxiv. and xxv., particularly vol. xxv. p. *13. 



J- De Candolle, Physiologie Vegetale, p. 157. 



