F. KiDD AND C. West 23 



the factors which influence the plant during its earliest stages of develop- 

 ment, have a more or less pronounced effect upon the whole of its 

 subsequent life-history. 



In the first chapter of this review we dealt with the factors which 

 acted upon the plant whilst still a seed upon the parent. The most useful 

 criterion here was found to be the size of the seed. A large amount of 

 work bearing upon the effect of the size of the seed upon the growth and 

 yield of the plant produced was reviewed, and an endeavour w^as made 

 to distinguish critically between genetic and physiological factors. A 

 certain amount of evidence was found indicating that the effects of the 

 parental environment of a seed were sometimes only visible in the 

 resulting plant. 



In chapter ii we dealt with the influence of the degree of maturity of 

 the seed at the time of harvesting upon its " potentiaUty," and came to 

 the conclusion that all comparisons made between mature and immature 

 seeds were vitiated by the fact that immature seeds deteriorate more 

 rapidly under storage conditions than mature seeds. In many cases it 

 was found that the yield per plant from immature seed was at least 

 equal to that from mature seed. 



In the third and present chapters we have dealt with the aspect of 

 the subject which is probably of most interest to the practical man, 

 namely, the effect of the conditions during germination and in the early 

 seedling stage upon subsequent growth and final yield. The work dealing 

 with the soaking of the seed in water or salt solutions was critically 

 reviewed in chapter iii. In the present chapter the most interesting 

 group of facts which have come under review appear to be those brought 

 out by the work of Gassner and others on the effect of low temperatures 

 in pre-determining the time of flowering of spring-sown winter cereals. 

 This effect of exposure to low temperatures is a very clear and distinct 

 phenomenon. While it still remains unexplained, it nevertheless bears 

 out the general thesis based on the evidence which we have collected 

 from various sources, namely, that the external conditions which obtain 

 during the early stages of the development of the plant have a very pro- 

 nounced effect upon its subsequent development. The results of Gassner's 

 investigations show clearly that it is during the first few hours of ger- 

 mination that the " pre-determination phenomenon" can be most easily 

 and quickly brought about by exposure to cold. As the seedling develops, 

 the duration of the exposure to cold and the degree of cold necessary to 

 ensure flowering in the same year rapidly increase. 



While much is known with regard to the effect upon germination of 



