HOW PLANTS EAT. 51 



Some plants are annuals, and some perennials. 

 When annuals have flowered and set their seed 

 they wither and die. But perennials go on for 

 several seasons. Most of them, however, in cold 

 climates at least, shed their leaves on the approach 

 of winter. But they do not lose all the valuable 

 material stored up in them. Trees and shrubs 

 withdraw the starchy matter into a special layer 

 of the bark, where it remains safe from the winter 

 frosts, and is used up again in spring in forming 

 the new foliage. This new foliage is usually pro- 

 vided for in the preceding season. If you look 

 at a tree in late autumn, after the leaves have 

 fallen, you will see that it is covered by little 

 knobs which we know as buds. These buds are 

 the foliage of the coming season. The outer part 

 consists of several layers of dry brown scales, 

 which serve as an overcoat to protect the tender 

 young leaves within from the chilly weather. 

 But the inner layers consist of the delicate young 

 leaves themselves, which are destined to sprout 

 and grow as soon as spring comes round again. 

 Even the scales, indeed, are very small leaves, 

 with no living material in them ; they are sacri- 

 ficed by the plant, as it were, in order to keep 

 the truer leaves within snug and warm for the 

 winter. Nor do the autumn leaves fall off by 

 pure accident ; some time before they drop the 

 tree arranges for their fall by making a special 

 row of empty cells where the leaf-stalk joins the 

 stem or branch ; and when frost comes on, the 

 leaf separates quietly and naturally at that point 

 as soon as the valuable starchy and living mate- 

 rial has been withdrawn and stored in the perma- 

 nent layers of the bark for future service. 



Smaller and more succulent plants do not 



