334 Colchicine 



third period. Large-scale production of nionoploids is a discovery 

 for the future. 



The frequency of increasing nionoploids has been improved by 

 special methods adapted for a few species. Twin seedlings proved to 

 have a high incidence of monojiloids in Hax, cotton, and peppers. 

 The nionoploids derived from the twin embryo method were isolated 

 and doubled to make the homozygous diploids. i'^'^*- -'" As a basis for 

 improving commercial varieties some application has been made in 

 this direction.-'' Since many seeds can be rini over the germinators, 

 more nionoploids are discovered than was jjossible by field selection. 

 Gossypiuin was treated by these methods.''' 



Significant differences in the frequencies of nionoploids ha\e been 

 found with certain stocks of maize. Previously selected strains were 

 better than imselected ones. Oi:)en-pollinated varieties, generally, 

 were comparatively low for production of parthenogenesis.-''^ By ap- 

 propriate genetic markers, introduced from the pollen parent, the 

 detection of nionoploids at seedling stages is improxed. Color genes 

 from the pollinator are expressed in the diploid, but not those from 

 the maternal nionoploids. Cytological confirmation of the niono- 

 ploids among the colorless seedlings proved that the marking system 

 was reliable. 



Monoploid sugar beet obtained from seed taken from a colchicine- 

 treated shooting plant has been found. Their occurrence is quite 

 rare. In another instance, the nionoploids were derived from colclii- 

 cine-treated populations. An interspecific hybrid of Nicotiana pro- 

 duced two niono))loid ])lants. One of the plants was like one parent, 

 N. gJutinosa, and the other like A^ rcpauda. In the original cross the 

 former parent was the female type and latter was used as the polli- 

 nator. 



An important use for colchicine arises for making autodiploids 

 from monojiloids, thereby increasing the niunber of plants that can 

 be proj^agated. By spontaneous doubling some sectors regularly pro- 

 duce viable pollen and eggs. Injecting 0.5 ml. colchicine into the 

 scutellar node of the monoploid seedling jjroved to increase the 

 amount of good pollen ]jroduced. an index of doubling."'' A luiique 

 feature and application of the autodiploids of maize arises from the 

 fact that genetic systems are fixed as gametes and testable as such. 

 1 hereafter the autodiploid reproduces the fixed system of genes. 



13.4: Conclusion 



The nmnber of autoploids is larger than that of the amphi|)loids. 

 Rel'erence niunbers in this chajjter and other chajiters will be uselid 

 to check the many kinds of plants already studied. The \()liunc of lit- 

 erature has de\ eloped so extensively that every example coidd not be 



