CHAPTER II 



THE GROWTH OF THE SHOOT FROM THE BUD 



AFTER the emergence of the cotyledons above ground, the first 

 bud or plumule is to be seen between them. This is the germ of 

 the shoot and it develops into stem and leaves. That the plumule 

 does give rise to the stem and leaves may be ascertained, first, by 

 watching the growth of the young seedling ; and secondly, by 

 examining the structure of the plumule. As soon as it appears 

 above the cotyledons in a young seedling, it should be cut length- 

 ways through the middle and examined with a hand lens. It 

 will be found to consist of a central portion and of lateral out- 

 growths. This central portion is the stem ; the lateral outgrowths 

 are the leaves. All buds consist of these two parts, however 

 variously modified the leaves may be. 



INFLUENCE OF LIGHT. The main function of the stem is to 

 bear the leaves in such a way that they can obtain light, without 

 which it is impossible for them to do their work. The first leaves 

 of the seedling, the cotyledons, if they come above ground, are 

 also dependent on light for the performance of their functions. 

 In watching the growth of a seedling, it will be found, if accurate 

 records are kept, that one of the most important factors in its 

 development is not the intensity only of the light to which it 

 is exposed, but even more the duration of the hours of sunshine 

 each day. The intensity of light can be measured by an ordinary 

 exposure meter such as photographers use, and the hours of sun- 

 shine are obtainable from meteorological offices. 



The influence of light on colour is a matter of common experi- 

 ence. Any one who has watched a tree in the spring must have 

 noticed that the buds as they unfold have yellowish-green 

 leaves ; the same thing is seen in seedlings. When the cotyle- 



VOL. III. 3 



