ON THE DIRECTION OF PLANTS. 



257 



zontal, because the influence of gravity on the nutrient juices is then 

 so much the more considerable. But if the inferior side of an oblique 

 branch is nourished better than the superior one, the effect ought not to 

 be limited to an enlargement of the layers, but it should also elongate 

 the fibres,, for these two results always take place simultaneously as 

 long as a new shoot is capable of being elongated. The inferior side of 

 the branch will tend then to lengthen itself more than the superior: if 

 it could be made to grow separate, each of the sides would elongate 

 itself in proportion as it was nourished, but they cannot be separated ; 

 the fibres of the side the worst nourished continue shorter than the 

 others, and must draw them from their own side towards that part 

 which is most flexible, that is, towards the summit. Thus the branch 

 must always right itself in an upward direction, and this with so much 

 the more energy as it approximates the horizontal position. 



It is natural to conceive, that, if a stem or branch be compelled to 

 right itself, whatever be the extent of its obliquity, nothing but 

 straight branches would be found, or branches tending to become so. 

 The exceptions to this law are, for the most part, more in appearance 

 than in reality. In a certain number of plants the stem is so weak, 

 that although its extremities are tending to rectify it, still the base 

 sinks under its own weight. This is what happens in a variety of 

 degrees to plants that are either procumbent or ascending, and the 

 infirmity is so much the more striking as the stem is softer, or as it- a 

 elongation has been the more rapidly effected. 



In all this it is necessary to make our examination only into what 

 takes place during the first year ; it is then that the branch is length- 

 ened, and when it comes to be hardened afterwards, it generally keeps 

 the position which it had assumed during its development. 



The branches of trees follow the same laws ; at first the tendency is 

 to raise themselves as they are elongated ; then they direct themselves 

 downwards towards the horizontal line for two reasons : 1st, the new 

 branches which are formed above them shelter them from the light, and 

 the inferior ones are warped laterally in order to have their share. 

 2ndly, the weight which they acquire when they become very long, 

 acting constantly on the end of a lever, draws them towards the 

 horizontal position. 



VOL. I.— NO. VI. (JUNE, 1833.) 



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