THE PLANT AND THE SEASONS 



863 



DISASTROUS EFFECTS OF A SUMMER GALE. 



aside in various parts of the plant. With 

 the coming of the autumn, however, the 

 vitahty of the leaf steadily dechnes, the 

 sap movements become very slight, and 

 the time has come for the organ to be 

 separated from the tree. So far-seeing 

 is Nature, that the leaf is scarcely deve- 

 loped ere preparations are commenced 

 for the severance of it from the twig. 

 Quite early in the history of the leaf at 

 the point of union between the stalk and 

 the stem, a special arrangement of cells 

 is foiTTied. This has been called the layer 

 of separation, and consists of a number of 

 cells running at right angles to the tissue 

 of older formation. The greater the age 

 of the leaf the more markedly does the 

 hne of separation appear, and as the 

 processes of assimilation begin to slacken 

 and the moisture evaporates, the severance 

 of the organ is only a matter of time. 

 Finally, the presence of organic acids so 

 weaken the cells that the leaf will perhaps 

 fall by its own weight ; in any case the 

 first gust of wind will be sufficient to 

 complete the fracture. 



When the stalk has becc^me detached 



it does not leave a raw and bleeding 

 wound behind such as would be produced 

 by the forcible pulling of the leaf from 

 the branches. The very layer of cells 

 which brought about the separation has 

 also ensured the welfare of the twig from 

 which the leaf has been removed. A thin 

 veil is spread over the point of cleavage, 

 so that there is never any open surface 

 exposed to the air at all. There are few 

 more beautifully contrived processes in 

 the natural world than this fall of the 

 leaf, with which the tree passes into its 

 winter rest. And so the leaves, often 

 brightly coloured as the result of the 

 chemical change wliich has taken place in 

 their tissues, flutter to the ground — there 

 to He until decomposition gradually 

 changes them into soft mould. In tliis 

 way a bed of fine rooting material is formed 

 for future generations of seedlings. 



It is, indeed, a wrong impression to 

 consider the autumn as simply a time of 

 decay, for much is accomphshed at that 

 pericjd by way of preparation for the 

 following spring. Pull a Chestnut bud 

 to pieces just before the tree loses its 



