§1] 



UPON THE RATE OF GROWTH 



425 



ments were made upon each species. In each experiment two 

 lots of seeds were placed together in a thermostat ; the one 

 being subjected to daylight, the other being kept in darkness. 

 The percentage of germination in the eight lots was as fol- 

 lows : — 



Experiment No. 1 . 

 Experiment No. 2 . 



The result seems decisive and has been fully confirmed by 

 LiEBBNBEEG ('84) and JONSSON ('93), not only for Poa but 

 certain other small seeds. 



According to Liebenbeeg the favorable action of daylight 

 is due rather to the alternation of high and low temperature on 

 the seed. Thus, while about 3% of Poa seeds germinate in 

 a dark chamber kept constantly either at 20° or 28° C, 91% 

 are germinated after 34 days in a dark chamber kept for 19 

 hours at 20° C. and for 5 hours at 28° C. In this case we have 

 to do clearly with a response to a particular stimulus of the 

 heat rays reminding us of the stimulus of alternating heat and 

 • cold necessary for the germination of certain animal statoblasts 

 or gemmules (Braem, '95). 



Among growing animals, studies on the effect of light were 

 early made by Edwaeds ('21), who concluded that tadpoles 

 would not develop at all in the dark. In this he went as far 

 from the truth in one direction as Higgenbottom ('50 and 

 '63) and Macdonnell ('59), who denied any difference of 

 growth in the light and in the dark, did in the other. The 

 work of Yung ('78) first revealed the exact truth of the 

 matter. This naturalist placed freshly laid frogs' eggs in 

 vessels, each containing 4 liters of water and 60 eggs. One 

 lot was placed in front of a Avindow, where, however, it 

 never received the direct rays of the sun. The other lot was 

 kept constantly in the dark. Otherwise the conditions of the 



