Callus Formation 477 



obtained two males and two females from 20 injected eggs and 

 observed that the combs and wattles of all were approximately 

 twice the normal size and that two tail feathers of the roosters 

 were greatly elongated. A hen, kept in a cage with one rooster, 

 laid one nonhatching egg every two or three days. 



Callus Formation 



Polyploidy can be induced in certain genera merely by wound- 

 ing a plant. Lindstrom and Koos by chance obtained a haploid 

 tomato plant which had arisen spontaneously and had twelve 

 univalent chromosomes. They decapitated this plant and re- 

 moved all the axillary buds that appeared. Petrolatum was 

 placed over the cut end to keep the tissue fresh, and a healthy 

 callus formed over the cut surface. Within two weeks adventi- 

 tious buds arose from the callus tissue, and many of them were 

 removed, rooted, and raised to maturity. In the callus tissue a 

 number of binucleate cells were observed, and in some of them 

 the two nuclei were observed to fuse. Probably as a result of 

 these binucleate cells, about 30 per cent of the adventitious buds 

 that were tested were found to be diploids. These diploid plants 

 obtained from the haploid by rooting the shoots that arose from 

 the adventitious buds showed twelve pairs of chromosomes and 

 were homozygous for all the genes investigated. Similar studies 

 were made by decapitating the diploids. From this wound tissue 

 about 30 per cent of the adventitious buds gave rise to tetraploid 

 plants. They showed low fertility and had forty-eight chromo- 

 somes, most of which formed quadrivalents. These polyploids 

 can be secured from the callus tissue in tomatoes that follows 

 an injury. 



In Nicotiana, another genus of the same family, callus tissue 

 does not form naturally as in the tomato. Greenleaf found that 

 by decapitating A^. sylvestris X tomentosa or N. sylvestris X to- 

 mentosiformis hybrids, and by covering the surface of the wound 

 with the growth hormone, indole-3-acetic acid in anhydrous lano- 

 lin (1 per cent), a callus tissue would be formed in which ad- 

 ventitious buds would arise. They developed into shoots which 

 were rooted and examined for polyploidy. Of 1973 plants exam- 

 ined, 270 or 13.7 per cent were tetraploid. About 1 per cent of 

 the shoots were octoploids, and some shoots with unbalanced 

 chromosome complements also arose. Interestingly, whereas in 



