Plants in Relation to Man 503 



kernels from different places on each of the selected ears should 

 be taken, and those ears, the kernels from which do not all 

 germinate or germinate slowly, should be rejected. In the 

 second place, seed illustrate clearly the fundamental laws of 

 heredity, which are just as effective in plants as in men and 

 other animals, but more rapid. " Like tends to produce like," 

 and seed selection should be guided therefore by the known 

 facts of heredity, if the best and most abundant products are 

 to be secured. The important facts are considered in the fol- 

 lowing section in connection with the study of the work of 

 Mendel, the pioneer in the investigation of the conditions that 

 determine the hereditary transmission of characters from parent 

 to offspring. 



SUMMARY 



Men secure improvements in plants by the following methods: 

 (1) by selection of variations that show the desired characters ; (2) by 

 cross-pollination; (3) by propagation of " sports." 



Cross-pollination is usually successful only between plants of the 

 same species. 



Cross-pollination between selected plants of a given variety is 

 used to maintain and improve the standard of the variety. 



Cross-pollination between plants of different varieties but of the 

 same species gives hybrids which may combine desirable charac- 

 teristics of each of the parent varieties. 



Cross-pollination between related species is rare but has produced 

 such valuable plants as the loganberry and plumcot. 



In most plant species the seeds come true to kind, as in wheat, 

 corn, and beans. In many, as the potato, strawberry, apple, and plum, 

 the seeds produce numerous " sports " widely different from the 

 parent plants. 



The navel orange and the nectarine originated as bud " sports." 



Plants which do not come true to seed are propagated by dividing 

 the parent plant, so as to use its buds for the origin of new indi- 

 viduals. Examples are found in the growth of potatoes from the eyes 

 of the tubers, strawberries from runners, blackcaps and raspberries 

 from tips, grapes from cuttings, oranges by budding, and apples by 

 grafting. 



Seed selection should begin with selection of the parent plants. 



