Introductory. 13 



outstrip others in growth, i. e., are more vigorous ' than 

 others. One pig in a litter very often grows slower 

 than any of the others, i. e., is more feeble and less vigor- 

 ous than any of the others. Feebleness is the opposite 

 of vigor. The most vigorous plant or animal usually 

 attains the largest size, and as a rule, is most satisfac- 

 tory to its owner. Vigor is promoted by a favorable 

 environment. It is usually greatest in rather young 

 plants and animals, and declines with advancing age. 

 It may be reduced by disease or improper treatment, 

 and when thus reduced is often difficult to restore. Re- 

 duced vigor tends to early maturity and shortened life, 

 and sometimes to increased prolificacy. 



10. Hardiness and Tenderness are terms used to ex- 

 press the relative power possessed by different plants or 

 animals to endure extremes in their environment. The 

 Oldenburg apple endures with little harm vicissitudes 

 of temperature that are fatal to many other varieties; 

 in other words, it is hardier as regards temperature 

 than many other varieties. The reindeer is hardier as re- 

 gards cold than the horse, but tenderer as regards heat. 

 The melon plant is hardier as regards heat and drought 

 than the lettuce, but tenderer as regards wet or cold. 



11. Health and Disease. A plant or animal is said 

 to be in health when all its organs (parts) are capable 

 of performing their normal functions. An organ in- 

 capable of doing this, or the being possessing such an 

 organ, is said to be diseased. 



12. The Cellular Structure of Living Brings. A bit 

 of vegetable or animal substance, examined under a 



