1914] 



CROCKER &• DA VIS— DEL A YED GERMINA TION 



305 



the coat. Since the embryo has two arms of about equal length, 

 the imbibitional and osmotic swelling would cause the embryo to 

 extend 20 per cent the length of the seed beyond the limits of the 

 coat. The rapid elongation of the freed embryos is brought about 

 in part by the rapid swelling of the pectic walls. These facts force 

 one to believe that delay in germination in the Alisma seed is caused 

 by the seed coat preventing the complete imbibitional and osmotic 

 elongation of the embryo. If one assumes that, on the average, the 

 embryo in the soaked intact seed has elongated only 3-4 per cent 

 of its air-dry length, and this is probably not far from correct, one 

 sees that in the soaked condition of the seed the embryo is in 

 water equilibrium with 2 volume mol. cane sugar solution. Such a 

 solution has an osmotic pressure exceeding 100 atmospheres accord- 

 ing to later estimates (24, 27). This probably gives a rough 

 estimate of the force with which the embryo is pressing against the 

 coat in the intact seed lying in water. 



TABLE X 



Elongation of 8 Alisma embryos soaked in water 5 hours and then transferred 

 to 2 volume mol. cane sugar solution. Seed coats removed from both ends of the 

 embryo. Temperature 25 C. 



Treatment of embryos 



Air dry 



5 hours in water 



5 hours in sugar solution 



2 5 



40 u u « " 



« 

 « 



u 

 u 



5 



Extreme individuals 



1. Air dry 



5 hours in water 



" sugar solution 



2. Air dry 



5 hours in water 



u u sugar solution 



2 r « « « u 



u 



5 



Total length of 

 embryos 



803 

 1050 



879 

 861 



863 



Average length of 

 embryos 



100.4 

 131. 2 

 109.9 

 107.6 

 107.9 



Length of embryo 



97.O 

 131. 2 

 Il6. 



114. 



103.0 

 128.O 



110.0 



III.O 



Percentage of 

 elongation 



30.8 



95 

 7.2 



7-5 



40.2 



19 5 



17-5 



24.2 

 6.8 



7-7 



X shows the changes in length brought about in 8 embry 



them k hour 



in water and then transferring them to 2 

 )r 40 hours. Five hours in water gives an 

 average elongation of 30 . 8 per cent, and in the extreme individuals 



mol 



