No. 4-] 



THE DEVELOPMENT OF ANIMALS. 



IQI 



for animals. In all cases the maximum lies 6 to 8 above 

 the optimum, and there is a very considerable decrease in the 

 rate of growth from the optimum to the maximum. This is 

 best seen in the following curve constructed from the above 

 figures for Lupinus albiis : 



5 



45 

 40 



35 

 30 



25 

 20 



'5 



IO 



\ 



\ 



3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 



FIG. 5. Curve of growth in length of the hypocotyl of Lnfinus albus at different temperatures 

 constructed from figures in Table IX. The ordinates represent growth in millimeters in 48 

 hours and the abscissae degrees Centigrade. 



The ascending limb of the curve is very similar to the 

 curves in Figs. 1-4. But the descending limb is much 

 longer ; in animals, indeed, it may be entirely wanting. This 

 indicates that while the general law of increase in rate of 

 growth is the same for animals as for plants, plants have in 

 general become adapted to resist temperatures farther above 

 the optimum temperature of development. May this not be 

 due to the fact that animals in general can and do retreat from 

 the higher temperatures of direct sunlight, while plants are of 

 necessity subjected to them ? Even developing embryos of 

 animals which possess no power of locomotion of their own are 

 placed so as not to be subjected to these high temperatures. 



It is rather interesting to find that the curves given above 

 resemble in general form the curves measuring the rapidity 

 of known chemical processes at different temperatures. See 

 Freer and Dunlap. 



