364 



GROWTH 



solution and the process will be repeated. By this means re- 

 markable life-like growths are obtained. (Details of preparation 

 are given in Part II., p. 399.) 



Botanists are agreed that osmosis plays an important part in 

 plant growth. An experiment is given in Part II., p. 399, to 

 illustrate the production of turgescence and consequent rigidity 

 as the result of endosmosis. Plant growth is conspicuously 

 associated with turgor, and depends in great measure on the amount 

 of water taken up. Another and more plausible explanation may 

 be given of the swelling of plant tissues. In Chap. VIII., p. 66 (3), 

 we mentioned the power of colloids to imbibe and compress water. 

 It is extremely probable that plant turgor may be due to this 

 imbibition, initiated by some alteration in the hydrogen ion con- 

 centration of the tissue. 



It has been definitely proved that animal growth is accompanied 

 by increase in water content as shown in Tables LXIX. and LXX. 



TABLE LXIX. 



WATER CONTENT OP HUMAN EMBRYO. (FEHLING.) 



TABLE LXX. 



WATER CONTENT OP FROG EMBRYO. (DAVENPORT.) 



In the later stages of growth and especially in the higher 

 mammals the ratio of water to solids tends to diminish. In- 

 hibition of growth occurs when means are taken to prevent the 

 entrance of water. For example, Loeb put Tubularia and Ceri- 

 anthus, which live and grow in sea-water having about 3-3-5 per 

 cent, salts, into a more concentrated mixture. He found, when 

 the concentration of salts in the water was 5-4 per cent., that 



