CHAPTER XVI. 



Growth and Reproduction. 



§ I. Facts of Growth. — In a well-known aphorism Linnaeus 

 noted that living organisms were not alone in their power of 

 growth. Crystals become centres for other crystals, till a large 

 mass results ; and the product, as every case of minerals shows, is 

 often both orderly and complex. But it can hardly be said that 

 an inorganic body has any control over or credit in its growth, 

 nor does the latter follow as the almost necessary consequence 

 of previous waste or liberation of energy. It is one of the oldest 

 generalisations, that the growth of organisms has a peculiar 

 method of its own, that of intussusception as distinguished from 

 mere accretion. The new particles which are taken in, more than 

 replacing previous expenditure, are not deposited upon the sur- 

 face of already established material, as is the case with a crystal, 

 but are intercalated in the interstices of previous particles. It 

 is of course unnecessary to enter here upon the long-continued 

 controversy, whether such structures as the cell-wall and starch- 

 grains of plants grow thicker or larger by accretion in crystal- 

 like fashion, or by intercalation which is supposed to be charac- 

 teristically organic. It is worth noticing, however, as Biitschli 

 points out, that if the living matter has the foim of an intricate 

 network, the fresh material of replacement or growth may be 

 added to the surfaces of the threads which make the web. Thus 

 what is roughly called intercalation may be more literally an 

 internal accretion. 



Hunger is a dominant characteristic of living matter. When 

 a unit mass or cell has been giving off energy in doing any kind 

 of work, its substance is chemically impaired, — less capable of 

 doing further work until new energy has been supplied by 

 nutrition. Some have even maintained that a simple organism 

 may be physically attracted to, as well as psychically by, its 

 food. The supply which the lifelong hunger of the protoplasm 

 demands, is frequently afforded in greater abundance than the 



