§ 1] UPON THE RATE OF GROWTH 305 



that of phanerogams is believed to be gained chiefly from the 

 air at all parts of the body, roots as well as stems and leaves. 



Since oxygen is of great importance for metabolism (p. 2), 

 it is naturally essential to growth. It is well known that the 

 lower the oxygen tension is, the more slowly do seeds germinate 

 and pass through their early stages of growth. Thus in an 

 experiment performed by Bert ('78, pp. 848-853) barley grains 

 which germinated and were reared at various pressures had 

 in six days the following dry weights : — 



On the contrary, as the oxygen pressure increases up to about 

 twice the normal, growth is accelerated, but beyond that point 

 growth is retarded until at about 7 atmospheres growth hardly 

 occurs. 



In older seedlings, observations upon which have been made 

 by WiELEE ('83), Jentys ('88)', and Jaccard ('93), atmos- 

 pheric pressure below the normal, even down to one-fourth or 

 one-eighth of the normal, appears to induce accelerated growth ; 

 likewise in pure oxygen at the atmospheric pressure growth is 

 as rapid as or somewhat more rapid than in the ordinary at- 

 mosphere. When, however, the oxygen tension is above the 

 atmospheric pressure or below one-eighth of the normal, growth 

 is retarded. It thus appears that an abnormal oxygen pressure 

 may accelerate growth, and as we shall see later, the same effect 

 is produced by other abnormal conditions. 



Among animals, also, the oxygen tension exerts an important 

 effect upon growth. This is shown by the experiments of 

 Raxjber ('84, pp. 57-65) upon the eggs of the frog. 



To get a variable atmospheric pressure Kauber used champagne flasks 

 in which were put the eggs and a little water. Through the air-tight cork 

 of the inverted flask one end of a U-shaped glass tube of proper length and 

 strength was passed. To the other end was fixed a funnel through which 



