jgig] ROSE— AFTER-RIPENING AND GERMINATION 283 



a number of different families, showed that acids in low con- 

 centrations, especially hydrochloric acid, are effective forcing 

 agents. Crocker and Davis (6) obtained similar results for seeds 

 of Amaranthiis (unpublished work) and Alisma. Bases are equally 

 effective for Sagittaria and Alisma, but not for AmarantJms. 

 According to Ottenwalder (22) bases exert an inhibitory effect 

 on seeds of Epilobium hirsutum. 



In those cases where a state of dormancy exists in the erribryo 

 itself (Crataegus and Mains), temperatures slightly above freezing 

 have been found effective in hastening after-ripening (7). In 

 Crataegus, as Eckerson (8) has shown, the hypocotyl becomes 

 more acid as after-ripening progresses; hence dilute acids hasten 

 after-ripening by acting upon the hypocotyl directly. 



Material 

 The seeds used in these experiments were gathered in the 

 summer or the fall of 1 916 and 191 7. Each year those of Sambucus 

 were all collected on the same day from neighboring plants. Tilia 

 seeds of the 191 6 crop were collected during October from trees 

 growing on the dunes at the southern end of Lake Michigan. The 

 191 7 crop was gathered during September from trees in the parks 

 of Washington, D.C. The seeds of Rubus were collected during 

 late June 1916 from neighboring plants of several varieties, but no 

 attempt was made to keep those of the different varieties separate. 

 Among the seeds of all 3 species were found many without embryos 

 or with defective embryos. In most cases this fact accounts for the 

 varying number of seeds used in the cultures. Approximately 

 , 60 per cent of Ruhus, 75 per cent of the 1916 Sambucus, and 80 

 per cent of the 191 6 crop of Tilia were viable. Not more than 5 per 

 cent of the 191 7 crop of Tilia and Sambucus were defective. 



Histology and microchemistry of seed coats 

 Sambucus: Endocarp. — The seed in cross-section shows in the 

 lignified endocarp 3 regions: (i) the outermost, consisting of 3 or 4 

 layers of cells of irregular size and shape, with thin walls and large 

 lumina; (2) a middle one of i or 2 layers of fibers in cross-section; 

 and (3) an inner one of i or 2 layers of fibers in longitudinal section. 

 Seed coat.— Thi?> consists of several layers of collapsed cells with 



