190 THE STORY OF THE PLANTS. 



while larger and larger in bulk, its trunk increas- 

 ing in girth, and becoming buttressed at the base, 

 so as to support the large head of branches and 

 the dense mass of foliage. For the boughs are 

 so arranged that a great crown of leaves is ex- 

 posed in summer to the sun and air at the outer 

 circumference of the dome-shaped mass ; and in 

 this way every leaf gets its fair share of light and 

 carbon, and interferes as little as possible with 

 the work of its neighbours. Old beeches will 

 grow to more than 100 feet in height, and live 

 for probably three or four centuries. At last, 

 however, their protoplasm grows old and seems 

 to get enfeebled; the trunk decays, and the entire 

 tree falls first into dotage, then dies by slow de- 

 grees of pure senility. 



The common vetch is another familiar plant 

 whose life-history introduces to us some totally 

 different yet interesting features. It belongs to 

 the wide-spread family of the peaflowers, to which 

 I have already more than once alluded, and it 

 takes its origin from a comparatively large and 

 rich round seed, not unlike a pea, whose cotyle- 

 dons are well stored with supplies of starch and 

 other food-stuffs. It sends up at first a short 

 spreading stem, which twines or trails over sur- 

 rounding plants, developing as it goes very curi- 

 ous leaves of a compound character. Each leaf 

 consists of five or six pairs of leaflets, placed op- 

 posite one another on the common stalk in the 

 feather-veined fashion. But the four or five leaf- 

 lets at the end of each leaf-stalk do not develop 

 any flat blade at all, and are quite unleaflike in 

 appearance : they are transformed, indeed, into 

 long, thin tendrils, which catch hold of neigh- 

 bouring branches or stems of grasses, twine 



