^1 UNIT IN AGRICULTURE 21 



5. Relative amount of soil-derived and air-derived plant food. 



6. Most important soil-derived elements: nitrogen, phosphorus 



and potassium. Ex. 46. 



E. ENEMIES OF PLANTS. 



1. Insects. 



(a) Biting insects, as potato beetle, cabbage worm, etc. 



(b) Sucking insects, as chinch bug, plant lice, squash bug, 



San Jose scale, etc. 



2. Diseases caused by certain bacteria, as fire blight in pear and 



apple tree. 



3. Fungus diseases, as brown rot on peaches, potato scab, rust 



on wheat and oats, etc. Ex. 47. 



4. Spraying to control insects and diseases. 



(a) Fungicides Bordeaux mixture, lime-sulphur, etc. 



(b) Poisons for biting insects Paris green, arsenate of 



lead, hellebore, etc. Ex. 48. 



(c) Contact remedies for sucking insects lime-sulphur, 



tobacco, carbon bisulphide, etc. 



5. Identification of injurious insects and preparation of collec- 



tion. Exs. 49, 50, 51, 52, 53. 



Note. This collection should be as complete as possible, well 

 mounted and increased from year to year. It should include all the 

 more common insect enemies of corn, wheat, potatoes, orchard fruits, 

 and garden plants. 



Literature. 



Bailey, Nursery Book. 



Farmers' Bulletins, Nos. 91, 99, 126, 132, 155, 227, 231, 264, 275, 



281, 283, 316, 320, 329. 

 Cyclopedia of American Agriculture. 



E. ANIMAL HUSBANDRY. 

 I. The Horse. 



1. Origin and brief history. 



2. The two principal types. 



