238 BOTANY FOR BEGINNERS CHAP. 



nodes. This ultimately forms an independent individual by the 

 intervening portion dying away. The off-set of the House-leek 

 becomes similarly detached, and forms a new plant. The stolon 

 of the Couch Grass performs the same function. In the axil of a 

 leaf of the bulb of the Tulip a new bud is formed which even- 

 tually exhausts the whole bulb, and carries on the life of the 

 plant. The Potato produces tubers at the ends of the stolons. 

 These tubers after a resting period develop into new plants. 



The Pilewort and some of the Lilies produce small buds, which 

 receive the name of bulbils, in the axil of foliage leaves. These 

 bulbils contain stores of reserve material, and drop off the 

 parent plant to produce new individuals. The leaves of the 

 Begonia and other plants will, if they come in contact with the 

 soil, produce buds which develop into new plants. 



The Biological Importance of Vegetative Reproduc- 

 tion. As long as the food supply is plentiful, and the surround- 

 ings are favourable, vegetative reproduction suffices. It is an easy 

 way of ensuring the propagation of the particular races of 

 plants in which it is possible. Gardeners use this method on a 

 large scale for the production of any favourable character which 

 a plant may show. It is said that if vegetative reproduction is 

 indulged in for a long time by a particular race of plants there 

 is a tendency for the race to degenerate. Most plants, however, 

 also reproduce their kind by organs which are produced in a 

 sexual manner. 



Sexual Reproduction. The male reproductive cell is the 

 generative nucleus of the pollen grain, and the female cell the 

 oosphere in the embryo-sac. The former is called the male 

 pronucleus, and the latter the female pronucleus. Neither of 

 these cells can alone produce a nfew plant, but the actual repro- 

 ductive cell is formed by their union. The union of the male 

 cell with the female cell stimulates the cell formed, and it 

 develops into a new individual which combines the good or 

 bad characters of the parents. Sexual reproduction differs from 

 vegetative reproduction in the fact of the cells, which produce the 

 new plant, being formed in special organs the pollen grain and 

 embryo-sac. The most important fact in sexual reproduction is 

 that in a single cell there should be stored up the potentiality of 

 the future plant, or in other words, a single cell should be able 

 to produce a perfect plant. 



