244 



THE RATE OF GROWTH 



[CH. 



actual increase of protoplasm we shall speak presently, but the role 

 of water in growth deserves a passing word, even in our morpho- 

 logical enquiry. 



The lower plants only Uve and grow in abundant moisture; lew 

 fungi continue growing when the humidity falls below 85 per cent, 

 of saturation, and the mould-fungi, such as Penicillium, need more 

 moisture still (Fig. 75). Their hmit is reached a little below 90%. 



Humidity ^ 



I. 75. Growth of PeniciUium in relation to humidity. 



Growth of PeniciUium (at 25° C.) * 



Among th^ coelenterate animals growth and ultimate size depend 

 on Httle more than absorption of water and consequent turgescence, 

 the process, she wing itself in simple ways. A sea-anemone may live 

 to ^n immense agef, but its age and size have Httle to do with one 



* From R. G. Tomkins, Studies of the growth of moulds, Proc. B.S. (B), cv, 

 pp. 375-^01, 1929. 



t Like Sir John Graham Dalyell's famous "Granny," and Miss Nelson's family 

 of CereiLS (not Sagartia) of which one still lives at over 80 years old. Cf. J. H. 

 Ashworth and Nelson Annandale, in Trans. R. Physical Soc. Edin. xxv, pp. 1-14 

 1904. 



