414 Lutz, Triploid Mutants in Oenothera. 



mediate between 0. lata and 0. yiyas, and this type is perhaps 

 the most common of all, but such forms invariably had 22 and 

 never 21 chromosomes 25 ). I found this to be the number for 

 25 offspring of 0. lata X 0. yiyas, the majority of which appeared 

 to combine the characters of some type of 0. yiyas with those of 

 0. lata. 



Lastly, hybrids do appear among the offspring of this cross 

 having vegetative characters closely resembling those of 0. yiyas, 

 as described by Gates for a 21 -chromosome plant said to be an 

 offspring of 0. lata X 0. yiyaSj but such hybrids have shown in 

 each of the 8 individuals which I have studied 20 ), a somatic chro- 

 mosome number of not less than 28 nor more than 30 --never 21. 

 The 9th hybrid which I found having a chromosome number in the 

 region of that of 0. yiyas had a few characters suggestive of 0. lata 



25) These observations do not agree with those of Geerts (16) who, as pre- 

 viously quoted, reported 21 chromosomes for both types of hybrids described by 

 de Vries, The number of individuals from which Geerts made his counts is 

 not stated in his report. 



If we should find that a plant of a given type of vegetative character may 

 have a certain number of chromosomes in Amsterdam cultures and another in those 

 of Cold Spring Harbor, we must then no longer expect agreement in the observa- 

 tions of investigators from different localities, and the results of no one worker 

 could thereafter be made of general application to the problems of mutation in the 

 Oenothera. I have recently determined the chromosome number precisely in two latas of 

 de Vries' culture and identification grown in 1911, and find it to be 15 in each case. 

 It is therefore probable that the lata parent of the Amsterdam cultures of 0. lata X 0. 

 ffigas had also 15 chromosomes. Then, if the male parent had 28 chromosomes, 

 and the processes of reduction and fertilization were normal, we should certainly 

 expect to find 21- and 22-chromosome hybrids in approximately equal numbers 

 among the offspring of this cross. In the Amsterdam culture of 133 plants, 08 hybrids 

 were of one type and 65 of another. Of the Cold Spring Harbor cultures in which 

 the chromosomes of 61 plants were studied, 25 hybrids were found to have 22 chromo- 

 somes, and 16 hybrids 21 chromosomes. (Other numbers also were represented, as 

 stated above. See p. 422.) Of the 9 plants in which the chromosome number was 

 determined only approximately, 5 had the vegetative characters of 21-chromosome 

 plants, and therefore probably had 21 chromosomes, as they appeared to have. If 

 such were the case, then the two cultures of this cross produced 25 hybrids with 

 22 chromosomes and 21 hybrids with 21 chromosomes. Considering the fact that 

 only 61 plants were studied, this is coming pretty close to expectation. However, 

 the chromosomes of 19 hybrids of the 1908 culture were not examined, and the 

 vegetative characters of the majority of this number were of the 22-chromosomc 

 type. It is therefore probable that the number of hybrids having 22 chromosomes 

 in the small Cold Spring Harbor cultures was considerably in excess of those 

 having 21 chromosomes. 



I hope to study the somatic chromosomes of the lata-gigas hybrid (Geerts' 

 '/a-Typus') of de Vries' culture and identification in the near future. 



26) Although these hybrids strongly resembled 0. yigas in the majority of their 

 vegetative characters, no one of them duplicated the vegetative characters of any 

 one of the various types of 0. gigas with which I am familiar in the same sense that 

 the 2 lata hybrids of this cross duplicated the vegetative characters of 0. lata. 



