iQig] 



ROSE— AFTER-RIPENING AND GERMINATION 



287 



coats either on or off, to germinate is not due to an inability to 

 absorb water is indicated by table III. The data given in this table 

 were obtained by soaking seeds in distilled water at room tempera- 

 ture until they had come to constant weight. Here again the 



TABLE III 

 Water-holding capacity of air-dry Tilia seeds 



Condition of seeds 



Coats off 



Coats on 



Coats on 



Coats on 



Coats chipped . 

 Coats chipped . 

 Coats chipped . 



Weight of 



air-dry seeds 



in gm. 



2848* 

 1540 

 ,7842 

 II98 



4963 

 5040 



I 9590 



Water 



absorbed 



in gm. 



I .2071 

 0.7841 

 0.4146 

 O . 4804 

 I .5020 



15717 

 1.918s 



Percentage 

 of water 

 absorbed 



93 

 36 



23 



22 



100 



104 



97 



95 

 40 



24 

 66 



38 

 50 

 93 



* Average of 4 duplicates. 



variations in the percentage of water absorbed are in part due to the 

 presence of seed coats which contain no endosperm and embryo. 

 Even with the coats chipped it is not always possible to eliminate all 

 empty coats or defective seeds. The fact that the coats interfere 

 with water absorption to a considerable extent is clearly shown in 

 the table. The fact that seeds with coats removed or chipped, 

 however, and with a moisture content approximately equal to their 

 air-dry weight will not germinate when placed on a moist sub- 

 stratum at room temperature, is sufficient proof that water absorp- 

 tion is not the only limiting factor to growth. 



That seeds that have been stored in the air-dry condition when 

 the seed coats are intact can be forced to germinate is shown by the 

 following experiment. Approximately 7000 seeds (200 gm.) of 

 the 19 1 6 crop, with pericarps removed and coats chipped, were 

 placed on moist cotton in large Petri dishes and kept at 4-6° C. 

 from March 24, 1917, to June 10, 1917, a total of 78 days. At the 

 end of that time and before being transferred to a higher tempera- 

 ture, several hundreds showed the hypocotyl protruding from the 

 endosperm for i . 5-2 . 5 cm. Of these, 100 were planted in soil in 

 the greenhouse and 71 per cent produced seedlings. A second lot 

 of 100 seeds was planted in soil out of doors, and 64 per cent 



