Whyte — 23 — Research in Vernalization 



with those of La Rue and Avery (1938) on immature excised embryos of 

 Zisania aquatica in artificial culture. 



Nutman's next investigation (1941) amplified the earlier observation 

 made by Gregory and Purvis (1938a) that ears harvested as early as 5 

 days after pollination produced viable grain, and the earlier observations 

 made on the development of immature barley kernels removed from the 

 plant by Harlan and Pope (1922, 1926). Although the smallest viable 

 grain found by Nutman was only one-sixteenth the weight of normal grain, 

 it was found that all plants whatever their original grain weight reached 

 approximately the same size at the end of their period of growth. Over the 

 greater part of the experiment the plants grown from dwarf grain exceeded 

 those grown from normal grain in (a) relative growth rate (on a fresh 

 weight basis), {b) rate of tiller production, and (c) rate of leaf formation. 

 These three results are attributed by Nutman to a single effect, namely, to 

 the rate of development of the meristem of plants grown from dwarf grains 

 being higher. 



Purvis has returned in the eighth paper (1944) in this series to the ver- 

 nalization of excised embryos. It had already been shown (Gregory and 

 Purvis 1938?^ that the excised embryo of rye when supplied with nutrient 

 salts and glucose responded to vernalization in the same manner as the 

 whole grain and to a comparable degree. Similar results had previously been 

 reported by Gregory and Purvis (1936 a), by Konovalov (1937) and by 

 Bassarskaja and Grossman (1941), and confirm Lysenko's statement 

 that the locus of vernalization lies within the embryo. Further, Purvis 

 ( 1940) demonstrated "that the isolated stem apex of the embryo, if supplied 

 with sugar and subjected to low temperature, regenerates the whole plant, 

 which shows itself to have been vernalized." McKinney and Sando ( 1935) 

 noted a similar result when they mutilated embryos before chilling, but main- 

 tained the contact with the endosperm. Gregory and De Ropp (1938) had 

 further shown that if sugar is omitted from the medium in which these ex- 

 cised embryos are grown, they remain unvernalized. The general conclu- 

 sions drawn by these British workers from their experimental results is 

 that the large accumulation of blastanin found by Cholodny (1936) in the 

 endosperm of maize does not play any essential part in the vernalization pro- 

 cess ; the embryo is capable of synthesizing any hormones that may be 

 necessarv for vernalization from external sources of carbohydrate in the 

 presence of inorganic salts, with possibly the aid of additional substances 

 already present in the embryo before imbibition. Embryos excised from 

 unsoakcd seed can still be vernalized, thus showing that the objection to 

 the excised embryo technique raised by Cholodny (1939) and quoted by 

 Whyte (1939) is not valid. 



Purvis enumerates the factors which can possibly participate in the 

 vernalization process as follows : 



o) the embryo and its constituents, 



b) the source of organic carbon. 



c) the source of nitrogen and the mineral salts, 



d) the effect of low temperature. 



Preliminary experiments conducted in 1939 comprised the subjection 

 of excised embryos to a low temperature for 6 weeks on agar media contain- 



