THE CASE OF THE PIGWEEDS 



239 



apparently due to food-supply is illustrated in Fig. 406. The 

 two weeds grew five feet apart, one in hard soil by a walk, 

 the other near a compost pile. They were of similar age. 

 One weighed J oz.; the other 4J Ibs., or 136 times as much. 



405. Heredity. Marked variations tend to be perpet- 

 uated. That is, immediate offspring are likely to retain 

 some of the peculiarities of their parents. This passing over 

 of characteristics from parent to offspring is heredity. 

 By "selecting the best" for seed the farmer maintains and 

 improves his crops. It is said that "like produces like." 

 This is true of the general or average features, but we have 

 seen that the reproduction is not exact. It is truer to say that 

 similar produces similar. Fig. 407 represents a marked 



407. The progeny of little and big plants. 



case of heredity of special characters. The plants on the 

 right grew from a parent 24 in. high and 30 in. broad. Those 

 on the left grew from one 12 in. high and 9 in. broad. (For 

 a history of these parents see "Survival of the Unlike," 

 p. 261.) 



406. Selection. There is intense struggle for existence: 

 there is universal variation: those variations or kinds live 

 that are best fitted to live under the particular conditions. 



