VI.] FUNCTION OF HAIRS. 



125 



touch (Foxglove) ; cobwebby, when the hairs are 

 long, very fine, and interlaced like a cobweb (Thistle, 

 cobwebby House- leek). The arrangement of the 

 hairs is also interesting. In some plants there is a 

 double row of hairs along the stem. In the Chick- • 

 weed only one. This, perhaps, serves to collect rain 

 and dew, and it is significant that the row of hairs 

 is always opposite to the flower-stalk, which also has 

 a single row. Now, the flower-stalk is for a con- 

 siderable part of its life turned downwards, with the 

 row of hairs outwards. This, perhaps, may account 

 for the absence of hairs on that side of the stem. 



Many leaves are clothed with woolly hairs while in 

 the bud, which afterwards disappear. Thus, in the 

 Rhododendron, Horse Chestnut, and other species, the 

 young leaves are protected by a thick felt, which 

 when they expand, becomes detached and drops off". 

 Many leaves are smooth on the upper side, while 

 underneath they are clothed with a cottony, often 

 whitish, felt. This probably serves as a protection 

 for the stomata. In some cases the hairs probably 

 tend to preserve the leaves from being eaten. In 

 others, as Kerner has suggested, they serve to keep off 

 insects — apparently with the special object of pre- 

 venting the flowers from being robbed of their honey 

 by insects which are not adapted to fertilise them. 

 Fritz Miiller, to whom we are indebted for so many 

 ingenious observations, gives an interesting case. 

 The caterpillar of Eunomia eagrus, when about to 

 turn into the chrysalis (Fig. 78), breaks off its hairs 

 and fastens them to the twig which it has selected, so 

 as to form on each side of itself about half a dozen 



