6 PJtysiolocfical Pre-fletermination 



barley, oats) not appreciably; (2) the growth of the resulting plant was 

 at first delayed; and (3) the experimental plants flowered earlier and 

 more freely than the controls. He also found that seeds after dry 

 heating were unusually sensitive to climatic and soil conditions during 

 germination. As a result of this growth-analysis Wollny appears to 

 have been doubtful as to the utihty from the economic point of view of 

 drying seeds. 



(6) Low Temperatures. 



Many authors have dealt with the effect upon germination of exposing 

 seeds in the moist condition to low temperatures. This has been found 

 to be a method of general application for stimulating the germination of 

 dormant seeds (cf. Kinzel(20)). 



The question as to what effect exposure to low temperatures during 

 the critical stages of germination may have upon the subsequent course 

 of development has been investigated in the case of seeds of the so-called 

 winter-cereals which normally germinate in late autumn, pass the winter 

 in the vegetative condition, and flower during the following summer. 

 If the seeds are sown in the spring, the plants produced do not complete 

 their development during the ensuing summer and autumn but they 

 flower and set seed only in the following summer. 



This behaviour on the part of winter-annuals has attracted attention 

 in relation to problems of rhythm and periodicity, the question at issue 

 being whether rhythm and periodicity in plants are inherent properties 

 of the protoplasm or the direct effects of external conditions. Without 

 entering into a discussion of the theories put forward by various authors 

 we may deal fully with the careful series of experiments recently carried 

 out by Gassner(iO)i at Hamburg, and published last year. Gassner 

 planted several winter varieties of cereals'- in the spring and investi- 

 gated whether exposure of the seeds during germination or of the 

 plants during the early stages of seedling growth to low tempera- 

 tures would affect their subsequent development. In the only com- 

 munication at present available this author confines his attention to 

 the time of formation of the flowering stems (culms) of the cereals 

 investigated. 



In each experiment four lots of 50 seeds ("pure line"') were germin- 

 ated on moist sand in crystallising dishes, which were kept at tempera- 



^ Cassncr gives a full list of references to previous work on this subject. 

 ^ For example, "Petkuser" winter rye; "Friedricliswcrtlirr Maiiiiniilir" uiiitci' 

 barley; "Svalofs Extra Squarehead" winter wheat, etc. 



