Vernalization and Photoperiodism — 36 — A Symposium 



Reference should be made to the original article for the method of meas- 

 uring maturity in conventional units. It is clear from these results that the 

 low temperature during the previous season had a marked efifect, although 

 Gregory and Purvis note that not all the treated grains had attained the 

 vernaHzed condition. Only 38 per cent of the treated grains produced plants 

 with fully emerged ears, although others were approaching that stage. These 

 data led to the same conclusion as that reached by Kostjucenko and 

 Zarubailo with regard to the sensitivity of an active embryo and the in- 

 sensitivity of a dormant one. 



Gregory and Purvis (1938a and b) dated the ears at anthesis and thus 

 determined the age of the treated embryos. The results of the experiment 

 showed that they could be grouped into 10-day classes covering the period 

 from 5 days to 35 days after anthesis. The treatment is effective from the 

 earliest stage of the development of the embryo, decreasing in intensity as 

 beginning of treatment is delayed. Low temperature is therefore effective 

 only while the embryo is actively growing, and ceases to be operative when 

 the embryo becomes dormant. Gregory and Purvis conclude that the 

 effect is quantitative, depending on the duration of the exposure to low 

 temperature as had been shown to be the case in normal vernalization 

 (Purvis and Gregory 1937). 



An important result which probably indicates how early a developing 

 embryo is fully sensitive to environmental conditions is that obtained by 

 Gregory and Purvis (1938 a and b), who showed that seed obtained from 

 ears removed from the parent plant as early as 5 days after anthesis ger- 

 minated after being sown in the following spring. Completely normal plants 

 were produced, although the individual immature grains were very small 

 (4X1 mm.) and had apparently no reserves. 



When winter rye was used, the plants grown from seeds having a range 

 of maturity of 5 to 50 days showed no difference in the stage of develop- 

 ment reached after 17 weeks. As the plants had not been vernalized, no ears 

 emerged. In spring rye, on the other hand, a variation was found in the 

 days from germination to anthesis varying from 51.8 ± 1.17 days (mean of 

 ten plants) in completely matured seeds, to 62.7 ± 0.91 days (mean of three 

 plants) in grain from ears removed 11 days after anthesis, the eariiest re- 

 moved ears to give viable grain. A decrease in the time taken to flower is 

 correlated with maturity of the ripening grain. Gregory and Purvis sug- 

 gest the possibility of partial devernalization of the very immature grains 

 of spring rye. 



Later studies made at the Research Institute of Plant Physiology, Lon- 

 don, have been concerned with a more detailed investigation of the pro- 

 cesses occurring in the embryo-sac of a cereal subsequent to fertilization, 

 and of the conditions of formation and the subsequent growth of dwarf em- 

 bryos of rye. Nutman's account of the former investigation (1939) is 

 concerned with the anatomical and cytological evidence for the formation of 

 growth-promoting substances in the developing grain of rye. 



In a later paper Nutman (1941) describes the formation of the dwarf 

 grain of rye in ears harvested at an immature stage, and compares the mor- 

 phology and anatomy of dwarf and normal grains and embryos. He con- 

 firms observations made by Gregory and Purvis with rye, and earlier by 



