GROWTH AND REPRODUCTION. 203 



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 centers 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 generalizations 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 surface 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 characteristically organic. 

 It is worth noticing, however, as Biitschli points out, that if the living 

 matter has the form 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 actual necessities require. There is a 

 surplus for further upbuilding after mere reparation has been made. 

 This surplus is the condition of growth. Popularly, but yet accurately, 

 it may be said that growth or addition to the capital of the organism 

 occurs when income is in excess of expenditure, when construction 

 preponderates over disruption. 



But beside this familiar fact it is necessary to place another 

 certainty — that of the limit of growth. We may fairly call giants a 



