PLANT PHYSIOLOGY 375 



sensitive Seeds," Bot. Gas., Ixxi, 1921, p. 249) has carried out 

 an exhaustive series of experiments with the object of determin- 

 ing the fundamental relation of light to the germination pro- 

 cesses of seeds. In these experiments the seeds were subjected to 

 a great variety of treatments, chemical, physical, and mechanical; 

 but no general conclusion can be drawn from his results, which, 

 however, demonstrate in a striking way the complexity of the 

 processes involved during the germination of seeds. 



The importance of temperature as a factor concerned in 

 the process of germination is emphasised by F. V. Coville 

 (" The Influence of Cold in Stimulating the Growth of Plants," 

 Smithsonian Report for 1919, pp. 281-91, Washington, 1921), 

 and by O. Munerati (" L'influenza delle basse temperature 

 sulla germinazione del frumento appena raccolto e dei semi 

 cosi detti freschi," Atti R. Accad. Lincei, Rendiconti, 1920, 

 [5], 29, p. 273). The former states that at ordinary summer 

 temperatures many kinds of seeds will not germinate, but 

 remain dormant until death overtakes them, whereas under 

 the influence of chilling they are stimulated to prompt germina- 

 tion. The case of the Bunchberry, Cornus canadensis, is 

 quoted. Seeds of this plant were sown on October 9, 191 2, 

 and after the winter chilling germinated promptly in the 

 following spring. A similar lot of seeds sown on the same 

 date, but kept in a greenhouse, the temperature of which was 

 not allowed to fall below 55° F,, showed no germinations after 

 twelve months. These seeds were then chilled for two months 

 at a temperature of 3 5^-40° F., and when brought back into 

 the greenhouse they germinated within a month. 



Munerati, working with seeds of Avena sativa and A. 

 fatiia, obtained immediately after harvesting 81 per cent, 

 germinations at a temperature of from 12° to 15° C, as com- 

 pared with 3 per cent, germinations at 32° to 35° C. 



When considering the question of delayed germination and 

 dormancy of seeds the subject of longevity of seeds naturally 

 arises. Loss of vitality may result from a number of causes, 

 such as the degeneration of enzymes, accumulation in the 

 cells as the result of various metabolic processes of substances 

 toxic to seed, exhaustion of food reserves through respira- 

 tion, etc. etc. Crocker and Groves (" Catalase and Oxidase 

 Content of Seeds in Relation to their Dormancy, Age, Vitality, 

 and Respiration," Jonrn. Agric. Res., xv, 191 8, p. 137) have 

 pointed out that the loss of vitality and death of seeds may 

 probably be due to " a time-temperature denaturing of certain 

 colloids in the embryo," whilst McHargue (" The Significance 

 of the Peroxidase Reaction with Reference to the Vitality of 

 Seeds," J ourn. A mer. Chem.Soc, 42, 1920, p. 612) has concluded 

 that the vitality of seeds depends upon the presence of a sub- 



