306 Colcbicina 



down on paper more easily than producing die plants. One step is 

 hybridization and the doubling ot chromosomes; the next procedure 

 requires some new approaches. 



Certain species are totally incompatible.^"' The tri-specics''' hy- 

 brids have overcome these difficulties, for some genomes can be 

 brought together in a tri-species hybrid not possible in a regular 

 hybridization. Gossypiuni arhoreum and G. harknessii have not been 

 brought together except when the hexaploid G. hisutum X <^- ^"^^o- 

 reum was crossed w'ith G. harknessii. In this manner a tetraploid 

 brought together genomes {AD) i A^ D. representing G. hirsiitiinu G. 

 arhoreum, and G. harknessii, respectively. Six new tetraploid tri- 

 species hybrids were developed by this method^'' (Table 12.2) . 



From a plant-breeding standpoint, amjihiploids incorporating 

 genomes of G. anomahim, G. raimondii, and G. liarknessii with the 

 commercial strains of Iiirsutum are promising and represent a new 

 attack on the problem of cotton improvement.''-^ Increases in fiber 

 strength are possible; however, a problem arises when one tries to 

 gain hi fiber strength and also maintain the good qualities necessary 

 for commercial varieties of hirsiitum. Much cytological work is 

 needed; integrating the theoretical knowledge with practical testing 

 appears to be the outstanding problem at the moment. A final j>rac- 

 tical contribution resulting from the incorporation of characters from 

 other species is promising. Numerous amphiploids have been made 

 in a short time. Much has been done with colchicine as a preliminary 

 to the larger work of sorting out, by polyploid breeding, gains from 

 accumulated knowledge. 



Among polygenomic hybrids, mosaics in flower and leaf appeared. ^^ 

 Increasing the number of chromosomes shows some increasing tend- 

 ency toward mosaicism, but number alone does not determine the 

 degree. This is a side problem with no specific explanation except 

 that the polyploids exhibit such characters.'- ^^ Another side prob- 

 lem is the somatic reduction in numbers of chromosomes within a 

 hexaploid species hybrid. An original plant with 78 chromosomes 

 developed sectors that were triploid, having 39 chromosomes. Per- 

 haps the method offers a way to extract useful components from a 

 complex hybrid. i^'' "- 



Aneuploids in Gossypixnn are readih de\eloped because the trip- 

 loids and jxntaploids are unbalanced types. Backcrossing and selec- 

 tion for trisomies and tetrasomics are possible among the synthetic 

 polyploids. Resultant ancuploid types have their effects upon leaf 

 texture, color, and structure. New lines with an extra pair of chromo- 

 somes, 54 instead of 52, may include Asiatic or American chromo- 

 somes placed into the opposite germ plasm.^'' 7?zh77specific and inter- 

 specific trisomies and tetrasomics were obtained. Such lines may be 

 partially stable, fertile, and morphologically distinguishable.^-^ 



