THE IMPORTANCE OF HAIRS IN PLANT LIFE 77 



Not only do hairs protect against too rapid transpiration, 

 but also against changes of temperature. The young leaves in 

 buds are often wrapped in white downy hairs which protect 

 them from the cold of winter, as in the White Beam tree, which 

 looks in the distance almost white from the thickness of the 

 cottony filaments on the under surface of its leaves. 



CLIMBING. Hairs, especially if hooked, help a plant to climb. 

 Hop-pickers dislike having to pick hops in wet weather, not only 

 because all outdoor work is pleasanter in a bright sunny atmo- 

 sphere, but on account of the way in which their hands get cut 

 by the hairs, which are much stiffer in damp weather. The leaves 

 of the Hop are covered with hairs, some of which are seen under 

 the microscope to have, as it were, two horned appendages. It 

 is these that enable the hop in its wild state to cling to any support 

 it may touch in the course of growth. Many of the genus Galium 

 are provided with hairs for climbing purposes. The best known 

 example is the Wild Cleavers, which is covered with small, stiff, 

 hooked hairs. Not only the stem and leaves are thus provided, 

 but the burrs are even more difficult to get rid of when once they 

 have attached themselves to clothing. Another species of Galium , 

 the Crosswort, also has closely packed hairs, though not with such 

 well-developed hooks. Both those plants, especially the Wild 

 Cleavers, are found abundantly in hedgerows. Without some 

 means of climbing they would probably be far less luxuriant in 

 growth, for their stems are weak and the plant would be very 

 likely to be trodden down. Prickles often have the same function. 

 Rose and Blackberry stems catch hold of other plants by means 

 of the prickles developed on them. The Blackberry is often found 

 entwined with clematis. If the two plants are untwisted it will 

 be seen that the Clematis has climbed by twisting its leaf-stalk, 

 the Blackberry by hooking its prickles on to the other plant. 



POLLINATION. Perhaps the most striking use of hairs is 

 their share in the work of pollination. One naturally dwells on 

 the part played by insects in the carrying of pollen from one flower 

 to another, and botanists have always been fascinated by the study 

 of the relation of plants and insects, but hardly enough emphasis 



