12 BOTANY. 



24. Other angles of divergence. — Other angles of divergence 

 have been discovered, and much stress has been laid on what is 

 termed a law in the growth of the stem with reference to the 

 position which the leaves occupy. There are, however, numer- 

 ous exceptions to this regular arrangement, which have caused 

 some to question the importance of any theory like that of the 

 ' ' spiral theory ' ' of growth propounded by Goethe and others 

 of his time. 



25. Adaptation in leaf arrangement. — As a result, however, 

 of one arrangement or another we see a beautiful adaptation of 

 the plant parts to environment, or the influence which environ- 

 ment, especially light, has had on the arrangement of the leaves 

 and branches of the plant. Access to light and air are of the 

 greatest importance to green plants, and one cannot fail to be 

 profoundly impressed with the workings of the natural laws in 

 obedience to which the great variety of plants have worked out 

 this adaptation in manifold ways. 



Exercise 5. 



26. Shoots of the horse-chestnut — Select shoots with strong terminal 

 buds, and with several ring scars indicating several years' growth. Sketch 

 a shoot, showing the ring scars, the leaf scars, the lateral and terminal buds, 

 the lenticels (small rough elevations scattered over the surface of the twig, 

 made up of corky tissue through which air is admitted). Note that the lat- 

 eral buds arise in the axils of leaves (above the leaf scars). Are there buds 

 in the axils of all the leaf scars on the shoot ? How do they differ in size ? 

 Note that the larger and longer ones, from which the lateral branches usually 

 arise, are usually situated near the terminal portion of each year's growth 

 of the shoot. There was not room for all of the buds to grow into branches 

 because they would be too crowded, and would shut out light and air. In 

 the struggle for existence some have outgrown others which remain dormant 

 ready to start growth if by accident the main shoot should be broken just 

 above them. 



Compare shoots which have borne flower-clusters for several years, and 

 determine what effect this has had on the character of the branching. 



27. Buds of the horse-chestnut. — Sketch in detail a large terminal bud. 

 Note the color and texture of the outer scales of the bud. Is the texture of 

 the outer bud scales such as to afford protection to the tender portion of the 

 bud within ? Is there any other means for protection of the buds ? 



