>€hap. XXL NATURAL SELECTION. 231 



Independently of colour, other trifling differences are some- 

 times found to be of importance to plants under cultivation, and 

 would be of paramount importance if they bad to fight their 

 own battle and to struggle with many competitors. The thin- 

 shelled peas, called pois sans parchemin, are attacked by birds, 24 

 much more than common peas. On the other hand, the 

 purple-podded pea, which has a hard shell, escaped the attacks 

 of tomtits (Parus major) in my garden far better than any other 

 kind. The thin-shelled walnut likewise suffers greatly from 

 the tomtit. 25 These same birds have been observed to pass over 

 and thus favour the filbert, destroying only the other kinds of 

 nuts which grew in the same orchard. 26 



Certain varieties of the pear have soft bark, and these suffer 

 severely from boring wood-beetles ; whilst other varieties are 

 known to resist their attacks much better. 27 In North America 

 the smoothness, or absence of down on the fruit, makes a great 

 difference in the attacks of the weevil, " which is the uncom- 

 promising foe of all smooth stone-fruits ; " and the cultivator 

 " has the frequent mortification of seeing nearly all, or indeed 

 often the whole crop, fall from the trees when half or two-thirds 

 grown." Hence the nectarine suffers more than the peach. A par- 

 ticular variety of the Morello cherry, raised in North America, is 

 without any assignable cause more liable to be injured by this 

 same insect than other cherry-trees. 28 From some unknown cause, 

 the Winter Majetin apple enjoys the great advantage of not being 

 infested by the coccus. On the other hand, a particular case 

 has been recorded in which aphides confined themselves to the 

 Winter Nelis pear, and touched no other kind in an extensive 

 orchard. 29 The existence of minute glands on the leaves of 

 peaches, nectarines, and apricots, would not be esteemed by 

 botanists as a character of the least importance, for they are 

 present or absent in closely-related sub-varieties, descended from 

 the same parent-tree; yet there is good evidence 30 that the 



24 l 



Gardener's Chronicle,' 1843, p. America,' pp. 266, 501 : in regard to 



806- the cherry, p. 198. 



25 Ibid-, 1850, p. 732. 29 . Gardener's Chronicle,' 1849, p. 



26 Ibid., 1860, p. 956. 755. 



2 ' J. De Jonghe, in ' Gard. Chronicle,' so < Journal of Horticulture,' Sept. 



1860, p. 120. 26th, 1865, p. 254 ; see other references 



28 Downing, < Fruit-trees of North given in chap. x. 



