EMBRYOGENESIS IN FLOWERING PLANTS 313 



to explain the latter phenomenon. According to Laibach (1925, 1929, 

 1931), the maternal ovular tissue exercises a fatal influence on the 

 growth of the embryo, but in Liinim, as in Datura, the embryo can be 

 kept alive if it is removed in time from its surroundings. Hiorth (1926) 

 suggested that these anomalous developments are to be understood as 

 disturbances in the physiological relation between the embryo and the 

 maternal tissue. Fagerlind (1944) and Blalceslee et. al, have referred 

 to the possible stimulatory eff"ect by the male parent in this connection. 

 But, as Satina, Rappaport and Blakeslee (1950) point out, the growth 

 processes in ovules from incompatible crosses still require elucidation. 

 In particular, the cause of the abnormal growth of the endothelial layer 

 in Datura is highly enigmatic; for, in compatible fertilisations, this 

 layer acts as a source of nutriment to the embryo while in incompatible 

 crosses it eventually has a destructive action on it. The growth of the 

 tumour stops when the cell contents of the endosperm and of the 

 embryo have been absorbed. No outward growth of the tumour has 

 been observed. The speed and intensity of tumour growth depend on 

 several factors such as the species and races used in the crosses. Large 

 swollen seeds, with a jelly-like substance but without tumours, may also 

 be found. In such seeds the endothelium as well as the contents of the 

 embryo sac is destroyed. 



Various attempts were made by Satina et al (1950) to prevent the 

 abortion of embryos in ovules in interspecific Datura crosses, but all 

 proved unsuccessful. These included the treatment of ovaries with 

 pollen extracts, the treatment of the pollen with vapours and solutions 

 of auxins, the treatment of ovaries with extracts of styles and ovaries 

 of selfed Daturas, the injection of different hormones, vitamin mixtures, 

 enzymes and nutrient media into the ovaries, spraying leaves with sugar 

 solutions containing enzymes, and the injection and spraying of malt 

 extracts. Tumoral tissues and embryo-sac contents from incompatible 

 Datura crosses were added to semi-synthetic cultures of normal 

 D. stramonium embryos and were found to have an inhibiting effect on 

 embryo growth; the inhibition varied from 52-100 per cent, the latter 

 causing the death of embryo. Extracts of ovular tumours have now 

 been prepared by Rappaport, Satina and Blakeslee (1950) and their 

 effects observed when they were injected into the embryo sacs of 

 incompatible crosses and selfed strains, Fig. 84. It has been ascertained 

 that, in tumours associated with embryo abortion in incompatible 

 crosses of Datura, a water-soluble thermostable substance, unrelated to 

 auxin, is present. This substance can inhibit the growth of selfed 

 D. stramonium embryos both in vitro and in vivo. The embryo-sac con- 

 tents of inhibited ovules contain a substance capable of inhibiting 

 another set of capsules. This substance is reported as having been effective 



