Introductory. 13 



One pig in a litter very often grows slower than any of 

 the others, i. e., is more feeble or less vigorous 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 satisfactory 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. Keduced vigor tends to early 

 maturity and shortened life, and sometimes to increased 

 prolificacy. 



10. Hardiness and Tenderness are terms used to express 

 the relative power possessed by different plants or animals 

 to endure extremes in their environment. The Olden- 

 burgh apple endures with little harm vicissitudes of tem- 

 perature 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 regards 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 incapable 

 of doing this, or the being possessing such an organ, is 

 said to be diseased. 



12. The Cellular Structure of Living Beings. A bit of 



vegetable or animal substance, examined under a micro- 

 scope of moderately high power, is seen to be made up 



