796 BIOLOGICAL EFFECTS OF RADIATION 



Gesneriaceae. — Figdor (17, 18) could not germinate seeds of any 

 species of Gesneriaceae that he studied except in Ught. In his first 

 investigation he placed seeds of Streptocarpus wendlandii, S. kirkii, S. 

 polyanthus, S. rexii, S. achimeni flora, Naegelia amahilis, Saintpaulia 

 ionantha, and Sinningia regina in light and dark germinators. In 10 

 to 23 days the seeds in light germinated, but there was no germination in 

 dark even after 2 months. Seeds in the dark germinated when trans- 

 ferred to light, some species more and some less promptly than if they 

 had been placed in light germinators immediately. Figdor later obtained 

 similar results with seeds of Klugia zeylanica, Monophyllaea horsfieldii, 

 Alloplectus sanguineus, Tydaea hyhrida var. grandiflora, T. lindeni, 

 Isoloma hirsutum, I. hirsutum multifiorum, Gesneria aurantiaca, G. 

 macrantha, Streptocarpus grandis, Naegelia zebrina, and Gloxinia hyhrida 

 erecta grandiflora. His first investigation was made at 18°C. and the | 

 second at 20°C. He did not study the effect of various constant or 

 intermittent temperatures. i 



According to Lehmann (62, pages 477 and 478), thoroughly after- 

 ripened seeds of Gloxinia (Sinningia) hyhrida which had been in dry 

 storage for S^'2 years still required light for germination. He concluded 

 that after-ripening these seeds did not modify their light sensitiveness. 

 Ottenwalder (81, page 795) could not induce germination of G. hyhrida 

 seeds in darkness by raising the temperature of the seed bed up to 40°C. 

 or by pricking the seed coats. Gassner (25), however, obtained about 

 6 per cent germination of Sinningia speciosa seeds in darkness on filter 

 paper moistened with distilled water, 43 per cent in darkness on filter 

 paper saturated with 0.01 molecule KNO3, and 53 per cent in diffuse 

 light on filter paper wet with distilled water. Ammonium salts, nitrates, 

 and nitric acid in proper concentrations forced the germination of 

 these seeds in darkness, but salts, acids, and bases not containing nitrogen 

 were not effective. 



Investigations to date indicate that there is no other plant family in 

 which the seeds are so consistently favored in germination by light as are 

 the seeds of this tropical and subtropical family. The germination of 

 Gesneriacean seeds, however, should be studied under many other condi- 

 tions in conjunction with light. 



Chloris ciliata. — No light-favored seeds have had more thorough 

 study than the achenes of the South American pampas grass, Chloris 

 ciliata, especially in respect to the effect of other conditions upon their 

 light-sensitiveness. 



Gassner (23) found that light acted as such, and not through its heat- 

 ing effects; for no constant temperature would substitute for light, and 

 light was effective even when it did not induce daily intermittent tem- 

 peratures. Many of the light and dark experiments were carried out at 

 constant temperatures varying not more than 1°C. 



