Chap. XXI. NATUKAL SELECTION. 217 



varieties are known to resist their attacks much better. 28 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 uncompromising 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 particular 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. 29 From some unknown cause, certain 

 varieties of the apple enjoy, as we have seen, the great ad- 

 vantage in various parts of the world of not being infested by 

 the coccus. On the other hand, a particular case has been re- 

 corded in whieh aphides confined themselves to the Winter Nelis 

 pear and touched no other kind in an extensive orchard. 30 The 

 existence of minute glands on the leaves of peaches, nectarines, 

 and apricots, would not be esteemed by botanists as a charac- 

 ter 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 31 that the absence of 

 glands leads to mildew, which is highly injurious to these 

 trees. 



A difference either in flavour or in the amount of nutriment 

 in certain varieties causes them to be more eagerly attacked 

 by various enemies than other varieties of the same species. 

 Bullfinches (Pyrrhula vulgaris) injure our fruit-trees by 

 devouring the flower-buds, and a pair of these birds have 

 been seen " to denude a large plum-tree in a couple of days of 

 almost every bud ;" but certain varieties 32 of the apple and 

 thorn (Crataegus oxyacantha) are more especially liable to 

 be attacked. A striking instance of this was observed in 

 Mr. Eivers's garden, in which two rows of a particular 



28 J. De Jonghe, in ' Gardener's 31 ' Journal of Horticulture,' Sept. 



Chronicle,' 1860, p. 120. 26th, 1865, p. 254; see other re- 



89 Downing, ' Fruit-trees of North ferences given in chap. x. 



America,' pp. 266, 501 : in regard to 3 Mr. Selby, in ' Mag. of Zoology 



the cherry, p. 198. and Botany', Edinburgh, vol. ii., 1838, 



2° ' Gardener's Chronicle,' 1849, p. p. 393. 

 755. 



