16 Frincijiles of Plant Culture. 



16. Reproduction is the increase in number of living 

 beings. It is one of the properties of protoplasm and is 

 es.sentially a process of division. As living cells mul- 

 tiply liy forming new cells, so living beings, which con- 

 sist of cells, multiply by the separation of a part of their 

 own cells, and this separated group of cells grows into a 

 complete organism like the parent. The higher plants 

 multiply by seeds (156), which are separated from the 

 parent plant, and each of which contains a young ]3lant 

 (.54). The eggs from which young birds are hatched 

 contain cells filled with living jarotoplasm, and the pro- 

 toplasm of the living young of mammals is separated 

 from the parent before birth. 



17. Reproduction is either Sexual or Non-Sexual. Sexual 

 reproduction can take place, as a rule, only ujjon the 

 union of cells of different sexes. It is not peculiar to 

 the animal kingdom, but occuis in plants also, and except 

 in rare cases, is necessary to the production of seeds that 

 are capable of germination f 2S). It is the only method 

 of reproduction in the higher animals. Sexual repro- 

 duction does not usually take place until the period of 

 most rapid growth has passed. Non-sexual I'eproduction 

 is indei)endent of sex. It results from the direct separa- 

 tion of a iDart of the parent, wliicli under favorable con- 

 ditions develops into a comj)lete indi\idual. It occurs 

 when plants multiply by means other than by seeds, as 

 by non-sexual spores (5.3), bulbs (352), stolons (348), 

 cuttings (35S), etc., and it is a common method of re- 

 production in certain of the lower animals, as plant lice 

 (aphid;e). 



18. Heredity and Variation. The offspring of a plant 

 or animal tends to be like the parent or parents. But no 



