Colchicine 473 



division at the time the sperm enters the egg. After fertilization, 

 meiosis of the egg nucleus proceeds and the second anaphase is 

 reached about 30 minutes after fertilization. If the eggs are re- 

 frigerated at 0° to 3° C just after fertilization, this second meiotic 

 division fails to proceed normally, and a diploid egg nucleus is 

 produced which fuses with the sperm nucleus to form the nucleus 

 of the triploid animal. In the second species about 45 per cent 

 of the treated individuals were triploids (Table 25), but in the 

 first species one experiment was practically 100 per cent success- 

 ful. When the first species was treated at temperatures of 34.2° 

 to 37.2° C for 5 to over 50 minutes, about 80 per cent of the 

 treated eggs developed into triploid larvae. 



Colchicine 



In addition to other environmental agents, various chemicals 

 have been tested in order, if possible, to get an agent that is more 

 uniformly effective than these other agents. In 1937, Blakeslee 

 and Nebel, independently and approximately simultaneously, 

 reported that extremely valuable results could be obtained by 

 treating plants with the drug colchicine. Since then, so many 

 investigators have used it on such a wide variety of plants that 

 it would be impossible in this book to approach a complete dis- 

 cussion of the results obtained. In general, we can say that it 

 has been highly successful in a wide variety of genera in pro- 

 ducing both auto- and allopolyploids and that it has even suc- 

 ceeded in woody plants that had not previously yielded arti- 

 ficial polyploids from any treatment. 



Other chemicals have been used since the discovery of col- 

 chicine, and a number have been found which produce more or 

 less the same end result. They include benzene, benzene vapor, 

 acenaphthene, veratrine, sulfanilamide, chloral hydrate, lack of 

 oxygen, sanguinarine hydrochloride, and various growth sub- 

 stances such as heteroauxin. It is very interesting to note that 

 although acenaphthene acts more slowly on Allium than 

 colchicine, it can be used to produce tetraploids on Colchicum, 

 although the latter, as might be expected, is not affected by 

 colchicine. 



One of the chief effects of colchicine on plant tissue is on the 

 chromosomes of cells in the earlier stages of division. Apparently 

 cells in the resting stage or in anaphase or telophase are not 



