Fig. 20. 



ON LEAVES. 481 



Many leaves are clothed with woolly hairs while in the bud, which 

 afterward 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 fertil- 

 ize them. Fritz Miiller, 

 to whom we are indebted 

 for so many ingenious 

 observations, gives an in- 

 teresting case. The cater- 

 pillar of Eunomia eagrus, 

 when about to turn into 

 the chrysalis (Fig. 20), 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 stiff fences, to protect it during its helpless period of 

 quiescence. 



Vaucher long ago observed, though he gave no reason for the fact, 

 that among the 3falvacem (mallows) the species which produce honey 

 are hairy, and those which do not are glabrous. 



If we make a list of our English plants, marking out which species 

 have honey and which have hairs, we shall find that we may lay it 

 down as a general rule that honey and hairs go together. The excep- 

 tions, indeed, are very numerous, but when we come to examine 

 them we shall find that they can generally be accounted for. I have 

 made a rough list of the species in the English flora which have honey 

 and yet are glabrous. It does not profess to be exactly correct, be- 

 cause there are some species with reference to which I was unable to 

 ascertain by personal examination, or by reference to books, whether 

 they produced honey or not. My list, however, comprised 110 species. 



Now, in the first place, of these 110 species, in sixty the entrance 

 to the honey is so narrow that even an ant could not force its way in ; 

 twenty are aquatic, and hence more or less protected from the visits 

 of ants and other creeping insects ; thus we shall frequently find that, 

 if, in a generally hairy genus, one or more species are aquatic, they 

 are also glabrous as, for instance, Viola palustris, Veronica anagallis, 

 V. beccabunga, and Ranunculus aquatilis. Polygonum amphibium is 

 peculiarly interesting, because, as Kerner has pointed out, aquatic spe- 

 cimens are glabrous ; while in those living on land the base of the leaf 



TOL. XXVII. 31 



