LECTURE XXII. 



REPRODUCTION. 



So far we have been mainly occupied with the means by 

 which the maintenance of the individual is attained. But we 

 have incidentally learned that the period during which the 

 life of the individual can be maintained is limited, though 

 the length of life may be widely different in different cases. 

 Thus some plants, annuals, do not survive a single season of 

 growth ; others, biennials, live through two seasons ; and 

 others, perennials, persist for a greater or smaller number of 

 years. But in any case any given individual eventually ceases 

 to exist. Inasmuch, however, as the various species of plants 

 continue to exist, it is clear that new individuals must be 

 constantly being produced, and it is the object of these con- 

 cluding lectures to study the various modes in which these 

 new individuals are produced, to study, in other words, the 

 Reproduction of Plants. 



In the first lecture (p. 6) it was pointed out that repro- 

 duction is one of the fundamental properties of living pro- 

 toplasm. The protoplasm of an individual possesses the 

 property of giving rise to a new individual, and this may be 

 effected in either of two ways ; in the one case by means of 

 cells, not specially modified for the purpose, forming part of 

 the body of the individual, somatic cells as we may term 

 them ; in the other, by means of specially modified cells, the 

 reproductive cells, which are usually set free from the indi- 

 vidual. The former process we term vegetative reproduction, 

 the latter spore-reproduction. 



