392 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



into prominence by J0rgensen (1928) whose observations on Solarium 

 nigrum have already been referred to on page 314. Following 

 interspecific or intergeneric crossings, similar results have been re- 

 ported in Brassica (Noguchi, 1929), Oenothera (Gates and Goodwin, 

 1930), Triticum (Nakajima, 1935), and a few other plants. 



Kihara (1940) found that in Triticum monococcum the frequency 

 of haploids could also be made to increase by merely delaying the 

 time of pollination. By applying pollen on the sixth day after 

 emasculation, he obtained two haploids among 10 plants; on the 

 seventh day, four haploids among 44 plants; on the eighth day, five 

 haploids among 18 plants; and on the ninth day, three haploids 

 among 8 plants. 



Yasuda (1940) injected aqueous solutions of Belvitan into the 

 ovaries of Petunia violacea. In ovules fixed and sectioned 3 days 

 after treatment, he observed some striking changes. In some cases 

 the nucellar cells 10 were found to have enlarged as the result of such 

 stimulation; in others the egg had divided once or twice, forming a 

 small proembryo ; and in still others the antipodal cells had increased 

 in volume. In explanation of the fact that division occurred only 

 in the egg and the other cells merely enlarged, Yasuda says that in 

 embryonic cells Belvitan promotes cell division, while in mature 

 cells it causes only a growth of the cell wall. 



Yasuda's observations, although interesting, are still in a pre- 

 liminary stage, for it is not clear whether the embryos he obtained 

 were haploid or diploid, nor does he mention if he succeeded in fol- 

 lowing them to later stages of development. 



In conclusion, it might therefore be confessed that so far we 

 have not succeeded in finding a suitable method for inducing par- 

 thenogenesis in higher plants. Although exposure to temperature 

 extremes and other shocks and pollination with X-rayed or foreign 

 pollen have apparently given some positive results in special cases, 

 the number of parthenogenetic plants obtained by these methods is 

 too small to warrant the deduction of a definite causal relationship 

 between the treatment and results. What is really needed is an 

 agent for producing haploid plants which will give positive results 

 with approximately the same consistency as colchicine does in pro- 

 ducing polyploidy. A logical method of approaching the problem 



10 These must really be the cells of the integumentary tapetum, for the nucellus 

 disorganizes at an early stage in all members of the Solanaceae. 



