476 TEXTBOOK OF BOTANY 



"stranded" on the spindle and not be included in the new nucleus. A 

 chromosome might break in two during the process of splitting, and the 

 remaining fragment might adhere to the other daughter chromosome or 

 be lost completely. 



Having predicted that such irregularities might occur in chromosome 

 behavior during ordinary mitosis in vegetative cells, one has only to turn 

 to the literature of cytology to learn that all of them actually do occur 

 in the growing regions of plants. Specialists who devote their time to the 

 study of cells either have seen them occurring, or the\' have made 

 observations from which no other logical inferences could be drawn. 



If the altered cell survives, it may become the forerunner of a sector 

 of tissue, a whole branch, a leaf, a root, or a part of a flower that differs 

 from other corresponding organs of the same plant. Some of the colors 

 and patterns of variegated leaves, the white branches of plants, and the 

 red roots of sweet potatoes (Plate 4) are easily observed results of such 

 changes in the vegetative cells of plants. In similar fashion the branches 

 bearing seedless oranges originate. The nectarine and the Starke delicious 

 apple are the results of mutations in vegetative cells. Many varieties of 

 sugar cane, potatoes, and other plants that propagate mainly by vege- 

 tative means are known to have originated by aberrations in ordinary 

 cell division. If the aberration occurs in the fertilized egg, the whole 

 plant will be different, since the fertilized egg is the forerunner of all 

 the other cells of a plant. 



When such a change occurs in the body cells of the higher animals 

 after they have developed bevond a very early embryonic stage, it 

 perishes with the individual in which it occurs. The reproductive tissues 

 in these animals soon become differentiated from the body (somatic) 

 tissues. In plants the situation is quite different. If the aberration occurs 

 in the growing tip of a stem, flowers may later develop from cells con- 

 taining the aberrant chromosomes. Or if it occurs in some organ of a 

 plant which propagates vegetatively, a whole plant containing the aber- 

 rant chromosomes may be obtained by this means, and all its flowers 

 would develop from altered cells. In either case, if the alteration in 

 chromosomes is a stable one, it is perpetuated in plants by sexual repro- 

 duction. The white flower of hibiscus shown in Plate 4 is borne on a 

 branch that grew from the stem base of a red-flowered plant. White- 

 flowered branches have developed from this side of the stem base an- 

 nually for the past 9 years. This aberration in the hereditary units must 



