I9I9] 



ROSE— AFTER-RIPENING AND GERMINATION 



303 



MuLLER (20) has recently pointed out that in various seeds that 

 germinate readily the outward pressure of the contents at the time 

 of rupture was but slightly greater than the breaking strength of the 

 water-saturated coat, and Crocker and Davis (6) have found that 

 seeds of Alisma are held in a dormant condition because the force 

 of the expanding contents is not sufficient to rupture the coats. 



TABLE XIII 



Seeds of Rub us Idaens with endocarp removed; 100 

 SEEDS per culture; temperature 18-23° C. 



Treated with acid 



May 4. 

 May 13. 

 May 13. 

 May 13. 

 May 24. 

 May 24. 

 May 24. 

 May 24. 

 May 24'' 

 May 24* 

 June 9. 



Percentage of germination after 



4 days 



2 

 24 



6 days 8 days 



Todays 



45 

 48 

 46 

 50 

 20 



22 

 40 

 46 



57 

 50 



70 



52 



84 



63 

 61 



20 days 



96 

 70 

 61 



55 

 88 



84 

 80 



88 



93 

 89 



95 



* In darkness. 



Failure to absorb water is not the hmiting factor, since both reach 

 saturation after about 5 hours' soaking. Two facts indicate that 

 Ruhiis seeds belong in the same class with Alisma. In the first place 

 they germinate readily once the endocarp is removed, and in the 

 second place even with the endocarp intact they absorb water 

 readily. Occasionally ungerminated seeds with the endocarp 

 removed have been found which when examined closely show no 

 break in the coat. This suggests that the inner pectinized layer 

 of the coat may play a part in the delay, either by limiting water or 

 oxygen absorption, or both. As already indicated, the removal of 

 the carbonized endocarp resulted in the rupture of the coat in 

 practically 100 per cent of the seeds. This renders extremely 

 difficult the determination of the part played by that structure. 



Table XIV shows that the substrata most favorable for germina- 

 tion of naked seed are cotton, filter paper, and quartz sand. An 



