DORMANCY IN SEEDS 75 



statement concerning a few of the more recent and more significant con- 

 tributions to the subject. 



" (A) Light favors the germination of a large number of seeds and fruits. 

 Among these are Viscum album together with many other Loranthaceae 

 and epiphytes, all Gesneriaceae studied to date, many grasses, various 

 species of Oenothera and Epilobium, Ranunculus sceleratus, Lythrum salicaria, 

 and L. hyssopifolia. Viscum album and Arceuthobium oxycedri will not 

 germinate at all without light. The former is killed in darkness within a 

 few weeks, while the latter endures darkness for a longer period. Of 964 

 species of seeds studied by Kinzel, 672 or about 70 per cent were favored 

 by light under the [very limited] conditions used in his experiments. 



" {B) Light interferes with the germination of many seeds and fruits. 

 Among these are several species of Phacelia and other Hydrophyllaceae, 

 3 species of Nigella, several species of Allium and most other Liliaceae. 

 Of 964 species of seeds and fruits tested, Kinzel found 258 inhibited by 

 light under the conditions of his experiments. 



"(C) Some seeds and fruits germinate equally well in light and dark. 

 This is true of the small grains, Zea mays, beans, clover, and many other 

 legumes. Of the 964 species investigated by Kinzel, 35 were indifferent to 

 light. 



" (Z)) Several conditions partly or entirely displace the effect of light in 

 light-sensitive seeds and fruits. 



"(a) After-ripening in dry storage reduces or entirely eliminates the 

 need for light in various light-favored seeds. Pea achenes [caryopses] kept 

 in dry storage for one year germinate almost as well in darkness as in 

 light. After-ripening partially eliminates light need in Chloris, Ranunculus, 

 Epilobium, and Oenothera achenes or seeds. The inhibiting effect of light 

 on Phacelia seeds falls with period of dry storage. 



"(b) Seed or fruit coats, or the hulls of grasses, increase the necessity 

 for light in the germination of some light-favored seeds. The hulls render 

 Chloris achenes light-obligate and increase the need for light in Poa. 

 Pricking the seed coats of Oenothera increases germination in darkness. 

 The coats also modify the action of light on light-inhibited seeds. Removal 

 of the seed coats from Phacelia seeds overcomes the inhibiting effect of 

 light. Pricking the coats causes 'lichthart' seeds of Nigella to germinate 

 in part. 



"(c) A full atmosphere of oxygen forces the light-obligate Chloris achenes 

 with hulls intact to full germination in darkness, and the light-inhibited 

 Phacelia seeds to full germination in light. 



"(d) Knop's solution substitutes for light in a number of light-favored 

 seeds. The nitrate of the solution is effective. The other salts of the solu- 

 tion are not effective. Nitrites, nitric acid, ammonium salts, and urea are 

 also favorable. Nitrates entirely displace the light need of Chloris achenes 

 with hulls intact at temperatures above 22° C. They also increase greatly 

 the germination at temperatures below 22° C, where light inhibits. Nitrates 



