LEAVES AND BUDS. 



137 



plants the leaves tend to fit together like the bits of glass in a 

 mosaic or the tiles in a pavement, so as to avoid shading each 

 other and to lose as little sunlight as possible. This tendency 

 is easily seen in (1) plants whose leaves are crowded together 

 and form a rosette close to the ground e.g. Daisy, Hawk- 

 weed, Plantain, London Pride ; (2) many plants with whorled 

 leaves e.g. Woodruff ; (3) twigs of many trees e.g. Horse 

 Chestnut, Beech, Elm, Lime ; (4) twigs of plants which creep 

 along a wall or bank e.g. Ivy. In Labiates (e.g. Dead- 

 Nettle) and Stinging-Nettles the lower leaves have broader 

 blades and longer stalks than the upper ones. 



Even when the " mosaic " tendency is not at first glance 

 apparent, careful study of the plant in its habitat, or home, 

 will often show adaptations for efficient light-catching. It 

 must, of course, be remembered that the strongest light does 

 not, in this country, come from directly above, but at an 

 angle, even when plants are growing on level ground. In 

 studying the plants dealt with in the later chapters of this 

 book, you should notice and try to account for the position, 

 stalk-length, shape of blade, and other arrangements of the 

 leaves, remembering that, besides the tendency to catch as 

 much light as possible, the forms of leaves are often influenced 

 by other causes the necessity to withstand high winds, to 

 carry away ram which falls on the blade, to catch the light 

 when growing in dense masses (e.g. grasses and plants grow- 

 ing among them in fields), etc. 



This interesting subject can only be studied by personal 

 observation ; any field, wood, hedgerow, or garden will afford 

 abundant material to illustrate the points here mentioned, 

 and to show how the arrangement and shapes of leaves help 

 plants in the struggle for light and air, which is keenest 

 where plants are growing in crowded fields or hedge-rows. 



171. Decay and Pall of the Leaf. Leaves which fall 

 before the vegetative season is over are caducous ; deciduous, 

 if they fall at the end of each season, as in most cases of our 

 forest trees ; persistent, if they remain on the plant for more 

 than one season, as in evergreens. The leaves of such plants 

 as G-rasses, Lilies, Irises, etc., simply wither on the stem, but 

 in most trees the fall of the leaf at the end of the vegetative 

 season is brought about by the plant itself. When the 



