38 SCIENCE PROGRESS 



the reverse effect. Weak solutions of potassium nitrate, on 

 the other hand, increased the percentage of germination at 

 all the temperatures tested. Thus it would appear that at 

 the lower temperatures light and nitrogenous substances do 

 not act in a similar way upon the germination of Chloris seeds. 

 Gassner also found that nitrates did not penetrate the seeds, but 

 were held back by a semipermeable layer of the testa. Hence 

 we must look for the direct effect of such substances upon the 

 germination of these seeds in changes produced in the testa, 

 and not in the embryo. 



The results of germination experiments published last year 

 by E. Lehmann (" Ueber die keimfordernde Wirkung von 

 Nitrat auf lichtgehemmte Samen von Veronica Tournefortii," 

 Zeitschr. f. Bot., xi, 191 9, p. 161) show how complex the pro- 

 blems ^of light-sensitive seeds may be. Under ordinary con- 

 ditions the seeds of Veronica Tournefortii do not germinate in 

 light, and at higher temperatures, e.g. 30° C, do not germinate 

 in the light or in the dark. Solutions of potassium nitrate act 

 favourably upon the germination of these seeds either in light 

 or in darkness, but their effect is much more striking in light. 



Treatment with potassium nitrate in light resulted in an 

 increase in the number of germinations of about 80-90 per 

 cent, as compared with controls in distilled water. It was also 

 found that the higher the intensity of light the greater its 

 retarding influence upon the germination, and that potassium 

 nitrate was unable to counteract the retarding effect of a light ' 

 intensity of 440 candle-power at a distance of one metre. At 

 30° C. the nitrate had no effect upon germination either in 

 light or in darkness. 



Seeds of Viscum album are generally supposed to require 

 a definite resting period of about five months before they are 

 capable of germination. This is disproved by Heinricher 

 (" Ueber den Mangel^einer durch innere Bedingungen bewirkten 

 Ruheperiode bei den Samen der Mistel {Viscum album, L.), 

 Sitgungsb. d. Kais. Akad. d. Wiss. in IVien, Math.-naturw. 

 Kl., cxxv, Abt. I, 191 6, p. 26), who states that, under suitable 

 environmental conditions, e.g. high relative humidity and 

 light intensity of 1,600 candle-power, mistletoe seeds can be 

 forced to germinate at any time during the winter. 



In the course of an ecological investigation on the ger- 

 mination of the seeds of various forest trees, Boerker {Univ. 

 Studies, Nebraska, xiv, 191 6, pp. 1-90) studied incidentally the 

 effects of light and of various other environmental factors. 

 Although he came to the conclusion that light plays a distinct 

 part in the problem of seed germination under natural con- 

 ditions, he was of the opinion that it acted indirectly by affect- 

 ing soil-moisture, evaporation, etc. 



