THE EVOLUTION AND VARIATION OF FRUIT PLANTS. 27 



mildew, black knot, rust, and yellows, are alarmingly prevalent. 

 The orange groves in the Azores ; the olive trees of Southern 

 Europe ; the mulberry growths of China and Syria, have sustained 

 great loss of vitality from an unusual development of black 

 mildews on the foliage. During the past year thousands of acres 

 of vineyards in Southern California have been destroyed by a new 

 mysterious disease that is not produced by any insect. The 

 habit of planting new trees in situations where the old have 

 perished is a peculiarly dangerous one to young fruit plantations, 

 arising from the spawn of fungi, which are often found deposited 

 in the old hidden stumps and decayed roots. Composts of 

 decayed leaves, twigs, and other vegetable material that strews 

 the ground, will also harbor injurious matter which may prove to 

 be a source of harm to a healthy growing plant. Insect enemies 

 are now increasing and more frequently invade orchards and 

 vineyards. The curculio, once only destructive to the plum, now 

 marks the peach, cherry, and apricot, as well as the pear, quince, 

 and apple. Increase in plant diseases is certainly an agent that 

 causes fruits to decline, as witnessed in the downy and powdery 

 mildew, black rot, and anthracnose which attacks the grape ; the 

 yellows and peach curl ; the leaf fungus and black rot of ihe plum ; 

 apple and raspberry rust ; apple and pear scab ; and pear, goose- 

 berry, and strawberry leaf blight. Fruit insect-pests are annually 

 increasing, now numbering at least a thousand in this country ; 

 so that a general knowledge of the elements and applications of 

 economic entomology seems to be desirable and almost necessary, 

 to ward off these causes of decline in varieties. Much degeneracy 

 is properly attributed to ignorance and want of skill and care in 

 cultivating. Sound trees can only be produced from seedlings of 

 first-class fruits : and the sooner a tree is transplanted after its 

 top is formed, the more favorable are the prospects of a healthy 

 growth and an unimpaired vitality. 



The decline in numerous varieties of fruits shows how impor- 

 tant is the attempt to produce new ones, and suggests the inquiry 

 why so few kinds of recent origin are worthy of special commen- 

 dation. New original varieties of fruit have a tendency to revert 

 to an ancestral form. Certain kinds propagated by seed not 

 crossed with another variety, sometimes degenerate on account of 

 increased liability to disease and from the want of the rich stimu- 

 lants they demand, but they do not run out or lose their distin- 



