Lutz, Triploid Militants in Ociiothcra. 



From such a cross we should expect to obtain 21- and k 22- 

 chromosome offspring in greatest number. However, should a 

 normally reduced female germ cell unite with an unreduced male, 

 we should have a 29-chromosome offspring resulting. Should an 

 unreduced female unite with a normally reduced male and produce 

 offspring, we should expect this plant to have 35 or 36 chromo- 

 somes, according to whether the combination was 28 -j- 7 or 28 -\- 8. 

 The comparative frequency of 29-chromosome hybrids among the 

 offspring of this cross would be some indication of the comparative 



character; --thus demonstrating that gigas 14 -4- ^ Lamarckiana 7 produces the 

 same type of offspring as Lamarckiana 1 -\- rf gigas 14. 



In all cultures of these two crosses we should certainly expect to find the 

 majority of the offspring to be intermediate, 21 -chromosome hybrids. But if it is 

 possible for 0. Lamarckiana and 0. flit/as each to produce unreduced female germ 

 cells occasionally, then the union of unreduced female with normally reduced male 

 germ cells should be expected to produce 28-chromosome offspring in the culture 

 of 0. Lamarckiana X 0. gigas, and 35-chromosome offspring in that of 0. yigas X 0. 

 Lamarckiana (g 14 -f- j 1 14 and ? 28 + <$ 7). 



While it is probable that all of the hybrids of de Vries' two cultures hav- 

 ing intermediate vegetative characters had also intermediate chromosome num- 

 bers, we do not know, for instance, what the chromosome number of the 

 "Zwerg-Mutante" (0. Lamarckiana X 0. gigas} may have been. The linear-leafed 

 forms in these two hybrid cultures are also of interest in this connection, since, as 

 de Vries has said (p. 756) they appear in pure cultures of 0. gigas. I have suc- 

 ceeded in counting the chromosomes approximately in but four linear-leafed 0. gigas, 

 and each was found to have28(?), or more properly speaking, a number in the region 

 of 28. Now. if the linear-leafed hybrids from de Vries' cultures of 0. gigas ^ 0. 

 Lamarckiana and (). Lamarckiana X O- giff as were of the same type, and we 

 should later find that such pure-bred forms and hybrids have each 28 chromosomes, 

 it would indicate that they are produced by the apogamous development of unreduced 

 female germ cells in the first cross, and from the fertilization of unreduced female by 

 normally reduced male germ cells in the latter cross. 



With regard to the expectations for 35-chromosome offspring 0. gigas X 0. 

 Lamarckiana there is almost no evidence to indicate what these should be. Under any 

 circumstances, since only approximately 17 or 18 plants of this cross came to flower in 

 de Vries' cultures, we might expect all of these to be intermediates. It is furthermore 

 possible that an individual with a somatic chromosome number as high as 35 may 

 never be produced, although we have seen that 4 plants, having 30 chromosomes each, 

 appeared in the 1908 culture of 0. lata X 0. gigas. If 0. gigas produces unreduced 

 female germ cells occasionally, the union of unreduced female with normally reduced 

 male germ cells (in cultures of 0. gigas pollinated by 0. gigas) should produce 

 offspring with 42 chromosomes. It seems improbable that an Oenothera with a 

 chromosome number as high as this will ever be found. However, our knowledge 

 of chromosome number in offspring of 0. gigas pollinated by 0. gigas is as yet 

 very limited, and it is too early to arrive at conclusions. 



Davis reported upon 12 offspring of 0. gigas X 0- Lamarckiana ("Notes 

 on the Behavior of Certain Hybrids of Oenothera in the First Generation." 

 American Naturalist, Vol. XLIV., Feb., 1910). 8 of the 12 were said to have 

 been similar to Lamarckiana and 4 similar to gigas in the rosette stage. 6 of the 

 former and 1 of the latter came to flower. These 7 plants were described as similar 

 to one another at maturity, so it is difficult to guess what their chromosome 

 numbers might have been. 



