176 THE VICTORIAN NATURALIST. 



The regular habit of the plant would alone be insufficient to 

 prevent a branch from growing abnormally in one direction, 

 thereby endangering the stability of the whole tree. 



It will also have been noticed in thickly-wooded districts that 

 the trees grow specially tall and straight, the lower part being 

 often as free from branches or leaves as a telegraph pole. Here 

 the only light received comes vertically, and light being a 

 necessity to the plant, only the topmost shoots have found 

 sufficient light for their existence. If, however, a tree in a 

 position not so crowded as to prevent free access of sunlight to 

 all its parts has its regular habit interfered with so that branches 

 disappear from the places where they would normally grow, what 

 is the process which enables it to regain its lost symmetry ? 



On looking at almost any tree taken at random, it will be found 

 that where a new shoot issues from a stem or branch of a few 

 years' growth, it proceeds from a portion of the wood which is 

 curved, and the new shoot appears on the outer or convex side 

 of the bend. A rough sketch of a tree will at once illustrate the 

 point. A drawing which showed branches proceeding from the 

 inward part of a bend on the parent stem would be at once 

 pronounced untrue to nature, but where the branches proceed 

 from the outer side of the curve the appearance is seen to be 

 quite normal. 



It appears, then, that usually before a new shoot arises upon 

 an old stem or branch such stem has a tendency to bend in the 

 opposite direction to that in which the new shoot is to grow. 

 Such a bend will be due to the force of gravitation, and more 

 particularly to the fact that one part of the plant is being 

 developed more quickly than another, causing it to bend over to 

 that side which carries the greatest weight. The new shoot 

 grows out in the opposite direction, and so the equilibrium is 

 restored. 



As to the process by which this is effected, it will be seen that 

 when a branch is bent, the part upon the outer or convex side of 

 tlie bend will have its individual fibres in a state of tension, the 

 fibres offering less resistance to an outgrowth than on the inner 

 or concave side of the bend where the substance would be more 

 dense and compact and unlikely to yield to any internal force 

 which might otherwise be capable of producing a shoot. It is, 

 then, upon the convex side of the bend that the new shoot 

 appears, and while the parent stem remains bent everything is 

 favourable to the flow of sap and consequent growth of the new 

 branch. If, however, the new shoot should become so strong and 

 heavy as to counterbalance the weight of its parent, the latter 

 would become less bent, the opening in its fibres towards the new 

 branch would become more contracted, the flow of sap somewhai 

 less free, and the progress of the offspring would thus be kept 

 within proper limits. 



