§1] 



UPON THE KATE OF GROWTH 



367 



agreeing closer with theory. On the whole, Table XL indi- 

 cates that it is the osmotic effect which retards growth. 



In tadpoles a similar retarding effect of solutions has been 

 observed by Yung ('85), wiio made solutions of 0, 2, 4, 6, and 

 8 grammes of sea salt in 

 1000 grammes of water, ^^° 

 and reared frog's embryos 

 in them. Other conditions 

 excepting concentration 

 were believed to be alike 

 in all experiments. In the 

 0.2% solution the tadpoles 

 developed at nearly the 

 same rate as in pure water. 

 In the denser solutions 

 there was a retardation in 

 development which in- 

 creased with the density 

 of the solution, so that in 

 the 0.8% solution the lar- 

 vae hatched out seventeen 

 days behind the normal 

 time. 



The effect of a sudden 

 change in the density of 

 the solution has been es- 

 pecially stu-died by True 

 <^'95). Beans, Vicia faba, 

 which had radicles from 

 17 to 35 mm. long, were 

 placed directly in the solu- 

 tions and held there so that 

 the cotyledons alone were 

 free. The cultures were 

 kept in the dark. When 

 the transfer was made sud- 

 denly to a 1% solution of 



potassium nitrate, it was observed that a mechanical contraction 

 •occurred, followed by a more or less prolonged period of retar- 



no 



100 

 90 

 80 

 70 



-30 

 -30 



-50 



-70 - 



-90 

 -100 



.05 .10 .15 .30 ,35 .30 .35 .40 .45 .50 



Fig. 99. — Curves of average increase per cent 

 of individuals (ordinates) of Dero vaga re- 

 producing, during 10 days, in solutions of 

 different salts, whose strengths are laid 

 off as abscissae. The data are taken from 

 Table XL. 



