DEVELOPMENT. 75 



Inheritance A particular kind of plant, therefore, may 

 retain its characteristics year after year, century after century, 

 age after age, if the conditions are not greatly altered, be- 

 cause the successor follows, in the course of its develop- 

 ment, the same lines as its predecessor did. It is thus by 

 hereditary transmission that the characters of plants are 

 perpetuated. 



Variation Selection. But the course of development 

 in the offspring is not always and in all cases the same as 

 in the parents. On the contrary, there is a certain range 

 of variation, by virtue of which a seedling plant does not 

 exactly reproduce either of the parental forms ; indeed, as it 

 is of mixed origin, it could not be expected to do so. The 

 limits of variation no one can tell; sometimes they seeui 

 very narrow; at other times we know them to be very wide. 

 Within short periods of time the amount of variations may 

 be inappreciable. Within geological periods the variation in 

 the course of development is sometimes so enormous that, 

 were there not evidence of the fact, it would be difficult to 

 connect the plants and animals that have gone before with 

 those which now exist. Living plants, then, are influenced 

 in the course of their development by two somewhat anta- 

 gonistic principles the hereditary principle which, on the 

 whole, tends to keep plants as they are, and the tendency 

 to vary, which is the source of that variation in character 

 which enables plants and animals gradually to become 

 adapted to altered circumstances. This is beneficial to the 

 cultivator, by affording him an opportunity of selecting the 

 varieties best suited for his purpose. It is by exercising 

 selection of this kind that Mr. Hallet succeeded in raising 

 his " Pedigree Wheat." He simply selected for sowing the 



