Studies of Teratological Phenomena. 83 



cleistogamous, hence, yielding races which are at once ahnost natural 

 pure lines. Varieties and species in this genus in manj^ cases are fertile 

 inter se, and the seed produced by one flower furnishes an abundance 

 of progeny, thus helping to eliminate the arduous technique of making 

 crosses. The species and varieties which were used in this study are 

 described by number. 



a) Description of material-species and varieties.- 



300 — 309 Nicoiiana tabacum fasciata (Fig. 10). Mutant derived from 

 "Cuban" variety of N. tabacum, J. S. Dewey , 1907. This race was obtained 

 from selfed seed of a mutant found growing in a field of Cuban tobacco 

 in the district of Partidos, near the town of Alquiza, Cuba in 1907. 

 J. S. Dewey, who was connected with the company on whose plantation 

 the discovery was made, describes the original plant as follows: 'Stem 

 fasciated; leaves 152, not over 8 cm. long when dry, flowers abnormal, 

 very little seed produced.' Owing to the cleistogamous nature of 

 N. tabacum, the strain from which the mutant arose was probably a 

 natural pure line, the characters of which were largely homozygous. 

 The isolation of pure true-breeding lines ot Cuban tobacco from a mixed 

 population by Hasselbring (1912) seems to substantiate such a claim. 

 And if this be true, hybridization had no part whatever in producing 

 the mutation. As only one fasciated plant occurred in the field, so far 

 as is known, and as this plant was homozygous and bred true upon 

 selfing for the abnormal character, the actual place in ontogeny at 

 which the change from the normal to the abnormal took place must 

 have been shortly after fertilization. If it had occurred later in ontogeny, 

 the fasciated character would have appeared first as a bud -sport. If 

 it had taken place before fertilization as the result of a disruption in 

 one of the cells involved in the maturation of the eg^ or sperm, a 

 double mutation would have been necessary (i. e., a similar single 

 mutation in both egg and sperm ancestry) in order to account for the 

 homozygous condition of the original mutant. In the latter case, the 

 element of chance is so great, that it is very improbable, even had 

 such mutations occurred, that it would have been possible for them to 

 unite, and had all the germ-cells of a whole plant changed, more than 

 one abnormality should have appeared. One may say, of course, that 

 on its first appearance, it was heterozygous and that the single plant 

 found was a representative of an F2 or possibly of a backcross. But 



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