iQig] 



ROSE— AFTER-RIPENING AND GERMINATION 



305 



Seeds in the soil are more exposed to attacks by fungi than those 

 on agar or cotton. Previous soaking shortens the time the seeds 

 must He in the soil before germination begins, and hence lessens the 

 chance for infection. Unsoaked seeds placed on moist cotton 



TABLE XV 



Effect of water supply xjpon germination of seeds of Ruhus Idaeiis; 



100 SEEDS PER culture; TEMPERATURE 20-25° C. 



Substratum 



Percentage of germination after 



6 days 



8 days 



Todays 



1 2 days 



16 days 



per cent agar* . 

 per cent agar*, 

 per cent agar*, 

 per cent agar* . 

 per cent agar*, 

 per cent agar* 



Soaked 24 hours, then in garden soil. . . 

 Soaked 24 hours, then on moist cotton. 

 Not soaked, on moist cotton 



37 

 22 



30 

 40 



35 

 32 

 12 



43 

 32 



49 

 5° 

 37 

 64 

 42 



52 

 36 

 64 

 66 



70 

 62 



50 



73 

 60 

 61 

 55 

 71 

 72 



* .Average of 2 duplicate determinations. 



absorb water easily, hence swell more rapidly than in the soil, and 

 moreover are less liable to infection. Under these conditions soak- 

 ing offers no advantage. 



Summary 



General. — Air-dry seeds of Tilia americana, Samhucus canaden- 

 sis, and Ruhus Idaeus do not germinate when placed on a moist 

 substratum at room temperature. In no case does water absorption 

 seem to be the limiting factor. Air-dry seeds planted in the soil 

 over winter give low percentages of germination. 



Tilia. — Seed coats are not the cause of dormancy, although 

 they may serve to lengthen the dormant period. A state of 

 dormancy exists in the endosperm or embryo, or both. 



Seeds with coats removed after-ripen at temperatures slightly 

 above freezing. At 0-2° C. seeds after-ripen, but do not germinate. 

 At 4-6° C. both after-ripening and germination take place. Seeds 

 after-ripened at 0-2° C. germinate readily at 10-12° C, but very 

 poorly at room temperature. Once germination has begun growth 

 proceeds best at temperatures above 12° C. 



