12 ELEMENTS OF AGRICULTURE 



with the ovule. Thereafter, the parent plant has no 



influence on it except to furnish food. 



If an ovule is not fertilized, it fails to develop into an 



embryo. When shelling peas, we often see small traces of 



peas two or three times as large as a pinhead. These 



were ovules that were 

 not fertilized. If an ear 

 of corn is to fill out, 

 every silk must receive 

 one pollen grain. Most 



Fio. 7. Ear of corn that grew on an isolated ears of COm have a few 

 stalk. Only a few kernels formed. Why? 



missing kernels because 



some embryos were not fertilized. The remarkable thing 

 is that ears are so well filled. (Fig. 7.) 



16. Sexual and Asexual Reproduction. When the new 

 plant is formed by the union of two bits of protoplasm, 

 it is called sexual reproduction. The two uniting proto- 

 plasts are called gametes. If the gametes come from dif- 

 erent plants, they are said to be cross-fertilized. If both 

 pollen and ovule are borne in the same flower, it is sell- 

 fertilized. 



Many plants reproduce from stems, roots or leaves. 

 Such reproduction is without sex, or is asexual. Potatoes 

 are reproduced by the tubers. Quack grass and Johnson 

 grass reproduce by root-stocks, or underground stems. 

 Sweet potatoes reproduce by roots; willows grow from 

 cuttings; white clover stems take root; wheat, oats, and 

 barley form large clumps by stooling. Most of the farm 

 plants that reproduce asexually also form seeds. 



The first experimental proof of sexuality in plants was 

 made in 1691, but little application of this knowledge 



