28S TREES ; THEIR FORMS AND L^^b., 



shoots are at that stage when the pressure referred to begins. Let us 

 take our penknife and carefully remove the central shoot by cutting it 

 at a point immediately above that at which all the shoots are given off. 

 AVe shall shortly thereafter discover that by removing this shoot 

 we have removed alike the source of pressure and the demand for 

 space, and that the remaining shoots — branchlets though they be — 

 will retain their erect posture in defiance of terrestrial gravitation ! 

 Our fourth law declares shade and lack of moisture to be inimical to 

 growth. We have already seen that moisture is necessary. We 

 have also seen that light plays an important part in the economy of 

 growth. That continuous shade, therefore, which is the partial 

 absence of light, is inimical to growth admits not of a doubt. 

 Nature produces nothing that is useless, however ; and by-and-by we 

 will sec for what beautiful purposes she employs shade. 



If we have not already promised to investigate the operation of 

 these laws in producing the forms of tree described, we are, at least, 

 under tacit obligation to do so. It will not be expected, however, 

 that we deal with every form in detail. The time at our disposal 

 does not admit of this, nor does the case require it. All the laws 

 enumerated do not act with equal and unvarying force during all 

 stages of a tree's history. The potency of one law often marks the 

 impotency of another. For example, where light is strong in 

 function, shade is weak in energy ; where growth is robust, gravity 

 is proportionately weak in effect. Cold will not injure where heat 

 enough is present, and concussion will not destroy where motion is 

 not violent. It is also useful to remember that the horizontal 

 attraction of light on growing parts of a tree, is not so strong at the 

 surface of the ground — especially if the surface is level — as it is 

 higher up the tree. Whether the attraction of light upon a growing 

 imrt is as the distance of that part from the ground, I am not 

 prepared to say, but from long observation of the friendly rivalry 

 that exists between light and gravitation in their relations to plant 

 growth', I have been led to entertain a suspicion that something of 

 this kind is the case. However this may be, it is certain that 

 horizontal attraction on growing parts is less potent when these parts 

 are situated low than when situated high on the tree, so that branches 

 given off from a trunk at a point near the surface are — unless they 

 assume an upward posture, and so become what the forester calls 

 ' limbs ' — doomed to comparatively early extinction. This accounts 

 for the obconical appearance presented by the lower half of the form 

 of tree first described — an appearance due to listless horizontal 

 growth. To remove the evils of sickly growth in their lower 

 branches, Mv. Elvers invented a new method of training fruit 

 trees. Horticulturists are M-ell acquainted with the advantages 



