220 THE RATE OF GROWTH [ch. 



limiting factor in the growth of that micro-vegetation with which the whole 

 cycle of life begins. The tropical oceans are often very bare of these salts; 

 in our own latitudes there is none too much, and the spring-growth tends to 

 use up the supply. But we have learned from the Discovery Expedition 

 that these salts are so abundant in the Antarctic that plant-growth is never 

 checked for stint of them. Along the Chilean coast and in S.W. Africa, 

 cold Antarctic water wells up from below the warm equatorial current. It 

 is ill-suited for the growth of corals, which build their reefs in the warmer 

 waters of the eastern side ; but it teems with nourishment, breeds a plankton- 

 fauna of the richest kind, which feeds fishes preyed on by innumerable birds, 

 the guano of which is sent all over the world. Now and then persistent winds 

 thrust the cold current aside ; a new warm current, el Nino of the Chileans, 

 upsets the old equilibrium ; the fishes die, the water stinks, the birds starve. 

 The same thing happens also at Walfisch Bay, where on such rare occasions 

 dead fish lie piled up high along the shore. 



It is curiously characteristic of certain physiological reactions, 

 growth among them, to be affected not merely by the temperature 

 of the moment, but also by that to which the organism has been 

 previously and temporarily exposed. In other words, acclimatisation 

 to a certain temperature may continue for some time afterwards to 

 affect all the temperature relations of the body*. That temporary 

 c<!>ld may, under certain circumstances, cause a subsequent accelera- 

 tion of growth is made use of in the remarkable process known as 

 vernalisation. An ingenious man, observing that a winter wheat failed 

 to flower when sown in spring, argued that exposure to the cold of 

 winter was necessary for its subsequent rapid growth ; and this he 

 verified by " chiUing" his seedlings for a month to near freezing-point, 

 after which they grew quickly, and flowered at the same time as the 

 spring wheat. The economic advantages are great of so shortening 

 the growing period of a crop as to protect it from autumn frosts in a 

 cold chmate or summer drought in a hot one ; much has been done, 

 especially by Lysenko in Russia, with this end in viewf. 



The most diverse physiological processes may be afl'ected by 

 temperature. A great astronomer at Mount, Wilson, in California, 

 used some idle hours to watch the "trail-running" ants, which run 

 all night and all day. Their speed increases so regularly with the 

 temperature that the time taken to run 30 cm. suffices to tell the 



* Cf. Kenneth Mellanby, On temperature coefficients and acclimatisation, 

 Nature, 3 August 1940. 

 t Of. {int. al.) V. H. Blackman, in Nature, June 13, 1936. 



