EMBRYOGENESIS IN FLOWERING PLANTS 297 



(Caryophyllaceae), and Rocen (1927) observed starch grains in it in 

 Basel/a alba (Centrospermae : Chenopodiaceae: Basellaceae). 



In Dianthus, considerable quantities of starch and other reserve 

 foods are present in the placenta, ovary wall and ovule at the time of 

 fertilisation, the most conspicuous starch deposits being in the nucellus 

 prior to fertilisation and during the growth of the embryo from the 

 spherical stage to maturity. Deposits are first present in the funiculus 

 and extend to the micropylar end. Starch is abundant in the embryo 

 sac at fertilisation and is used in the early embryogeny. In ovules 

 containing well developed embryos, starch was still present in the 

 perisperm at the antipodal (i.e. cotyledon) end of the ovule, but not at 

 the micropylar end. This suggests that the mobilisation and uptake of 

 nutrients takes place by way of the basal or radicle end of the embryo, 

 Fig. 82. Dahlgren (1939) has given a list of angiosperms in which 

 starch has been observed in the embryo sac. Reserves of fat and 

 possibly of protein are present in the mature cotyledons and upper 

 hypocotyl, but there is no starch. 



AMINO-ACIDS IN DEVELOPING ENDOSPERM 



Species with large seeds like Zea mays lend themselves to investi- 

 gations of the metabolites present in the endosperm during the forma- 

 tion of the seed. These observations are of direct or indirect interest in 

 the embryonic development. Widely different types of maize all show 

 the same kinds of free amino-acids and amides, and in about the same 

 proportions, these substances being demonstrable in the endosperm at all 

 stages of development, subject to various fluctuations which have been 

 described. Most of the glutelin complex of proteins are formed during 

 the first half of the grain maturation period, and most of the zein 

 complex during the second half (Duvick, 1952) {see also p. 304) 



INDUCED PARTHENOGENESIS AND ADVENTIVE EMBRYOGENESIS 



Could parthenogenesis be induced in plants, it would be possible to 

 obtain homozygous, true-breeding types for genetical investigations 

 (East, 1930). The problem here is to find some substance, or treatment, 

 which will activate the ovum as the male nucleus does. Already in 1922 

 Blakeslee and others had shown the possibility of obtaining haploid 

 plants of Datura. Methods used to induce parthenogenesis include: 

 (i) exposure of flowering shoots to very high or very low temperatures, 

 or to X-rays; (ii) application of X-ray treated pollen, or of foreign 

 pollen to the stigma; (iii) delayed polhnation; and (iv) chemical 

 treatment (Ivanov, 1938; and Kostoff", 1941). Miintzing (1937) 

 obtained a haploid plant of Secale cereale by exposing the spikes to low 

 temperatures (0-3°C), and Nordenskiod (1939) got a similar resuh by 



