298 EMBRYOGENESIS IN PLANTS 



exposing them to high temperatures (41°-42°C). Haploids plants of 

 Triticum monococcum were found in spikes which had been exposed to 

 X-rays at the time of meiosis (Kihara and Katayama, 1932). When 

 Katayama (1934, 1935) pollinated the stigmas with X-rayed pollen 16 

 haploids were present among 91 seedlings. Other workers have been 

 less successful: Smith (1946) states categorically that he obtained no 

 increase in the number of haploids by X-ray treatment. 



The use of foreign pollen for stimulating parthenogenesis was 

 brought into prominence by Jorgensen (1928) working on Solatium 

 nigrum. The formation of haploid embryos following interspecific or 

 intergeneric crossing has also been reported in Brassica (Nogouchi, 

 1928), Oenothera (Gates and Goodwin, 1930), and Triticum (Nakajima, 

 1935), In Triticum monococcum, the frequency of haploids can be 

 augmented by delaying the time of pollination: when pollen was 

 applied on the sixth day after emasculation, 2 haploids were present in 

 10 plants; when appHed on the seventh day, 4 haploids were present 

 in 44 plants ; when applied on the eighth day, 5 haploids were present in 

 18 plants; and when applied on the ninth day, 3 haploids were present 

 in 8 plants (Kihara, 1940). 



Yasuda (1940) found that by injecting aqueous solutions of 

 'belvitan'^ into the ovaries of Petunia violaceae, some striking changes 

 took place in the course of three days. In some ovules the nucellar 

 cells enlarged as a result of the stimulation; in others, the egg divided 

 once or twice forming a small proembryo ; and in yet others the anti- 

 podal cells became enlarged. According to Yasuda the belvitan 

 promotes cell-division in embryonic cells but causes only cell-wall 

 growth in mature cells. It is not known if the small embryos thus 

 induced were haploid or diploid, nor if they were capable of further 

 development. 



From his survey of the investigations thus far reported, Maheshwari 

 (1950) concludes that a satisfactory method for inducing partheno- 

 genesis in higher plants has not yet been discovered. Various techniques 

 have yielded some results in special cases, but the number of partheno- 

 genetic plants so far obtained is still small: we cannot yet produce 

 haploid embryos at will with the consistency that polyploids can be 

 induced with colchicine. The difficulty seems to be that although the 

 egg can be made to develop parthenogenetically, no artificial means of 

 inducing endosperm formation is known. 



To be able to induce and rear adventive, i.e. nucellar, embryos, 

 possessing a genetical constitution identical with that of the parent, 

 would be of academic interest and practical value. In cultivated fruit 

 trees, such as Citrus spp., the method enables uniform root-stocks to 



* Belvitan: presumably a proprietary growth-regulating substance. 



