64 



pcjilodly (l('iii<»iish-a(('(l in (lie coiii-sr (»!' cxpci-iiiiciiljil work, iliat 

 are Avortliy of coiisideration al Hi is (iun.'. 1 want to mention 

 and very briefly discuss six of these: 



(1). Lateral or oblique condneiion. 



There seems to be a rather widespread (bnt erroneous) idea 

 that the crude and elaborated sap of a tree can pass up and 

 down the trunk or branch only in a longitudinal direction, that 

 is, lengthwise of the fibres or "grain" of wood or l)ark, or at most 

 with but slight deviation from this route. The fact that it is 

 transferred almost entirely in a longitudinal direction in a 

 healthy uninjured tree may be true enough under normal con- 

 ditions, but it is far from true in trees tliat have been injured 

 in certain ways, and, as all students of plant physiolog}^ know, 

 not strictly true under perfectly normal conditions. 



It is a fact of common knowledge that a tree will ordinarily 

 cover or grow over, an area of bare wood where the bark has 

 been removed. It is connnon knowledge to all observant persons 

 that these scars heal over mainly from tlie sides. In all prol)a- 

 bility this is largely because they adjoin the uninjured vessels 

 through which sap is being conducted in the normal longitudinal 

 direction, but doubtless in part also to other causes to which I 

 shall allude directly. If a partially or entirely healed over scar 

 should be dissected, it will be found that in the layers of wood 

 formed immediately after the injury the fil)res are curved out- 

 ward around the injury, and continue in a nearly longitudinal 

 direction l»ofli above and below tlie scar. When the scar is par- 

 tially covered, tlie newly formed fibres are sfraighter, and finally 

 after the scar is entirely covered, the youngest fibres will be 

 found to have assumed their normal longitudinal direction, or 

 very nearly so. 



If it were not for this possibility of oblique conduction, a tree 

 tliat had a large lesion extending half way around the trunk 

 on the nortli side, for instance, and an equally large one on the 

 south side, either above or below the other, would, to all intents 

 and purposes, be girdled. 



In the chestnut tree, the angle from the perpendicular to 

 which these fibres can be made to curve, as a result of experimen- 

 tal cuttings, may seem surprisingly great. In one instance the 



