I INTRODUCTION 27 



less oval leaflets, as iu AhIi, JMountaiu Ash, Eobinia 

 (Acacia of gardeners), etc. 



Palmate leaves form another type : as, for instance, 

 those of Sycamore, Maple, Plane, Guelder Rose. 



Jungner regards the palmate form also as an 

 adaptation to resist wind. He observes that species 

 with palmate leaves are particularly abundant in 

 windy countries and districts. The elastic stalks 

 enable them to arrange themselves so as it were to 

 turn their back to, and fly like flags in, the wind. 



As we have seen, the leaves of aquatic plants are in 

 many cases divided into filiform segments, thus exposing 

 a large surface to the action of the water. On the other 

 hand, floating leaves have a tendency to be circular. 

 Some plants have both these forms of leaf, — rounded 

 ones on the surface ; others finely divided, below. This is 

 the case, for instance, with some species of Ranunculus. 



Leaves growing in damp and shady places — shade 

 leaves as they may be called — are large, flat, smooth, 

 and delicate. Those of Petasites, Lactuca Scariola, 

 Dentaria, Orobus, Paris, Lunaria, Mercurialis perennis 

 (Dog's Mercury), Impatiens (Balsam), etc., belong to 

 this type. In dry, arid regions, such as the Riviera, 

 they would not survive a day. 



Another type of leaf may be called cricoid, as the 

 Heaths aflibrd typical and familiar examples. That of 

 Empetrum (Fig. 11) is a striking example. They are 

 evergreen, rolled at the edges, leathery, small, and 

 crowded. They suit cold and damp, and hot and dry 

 localities. To the former they are adapted, as they 

 present a smaller surface to the cold air, and especially 

 because, as the stomata open into the space which is 

 more or less completely enclosed by the rolled edges, 

 and are, moreover, also as a rule protected by hairs, 

 they are not liable to be clogged by moisture, but are 

 in a position to fulfil their important function as soon 

 as the sun comes out, and even to some extent during 

 rain. But though it is important that the power of 

 evaporation should be protected, it is, on the other 



