Feekuary 28, 1908] 



SCIENCE 



335 



chromosomes in the normal life history; it 

 is simply an abnormal ease of secondary 

 importance. Still it must be admitted that 

 in the case of apogamy, at least, the num- 

 ber of chromosomes is not the only factor 

 which determines the character of the 

 sporophyte and gametophyte. 



Further Studies on the Chromosomes of 



CEnothera: Dr. R. R. Gates, University 



of Chicago. (By invitation.) 



On account of the well-known variation 

 in chromosome numbers in root-tips, it was 

 important that the chromosomes of 0. gigas 

 should be counted in the germ cells. The 

 pollen mother cells of 0. gigas have 28 

 chromosomes, the reduced number being 

 14. In rare cases one chromosome passes 

 to the wrong pole of the heterotypic spin- 

 dle, making the numbers in the daughter 

 nuclei 15 and 13. 



This mutant is rare, having appeared 

 only four times in all cultures, only two of 

 these four maturing seeds. It is larger in 

 all its parts than the parent form, and this 

 is found to be due to the larger size of the 

 cells. The leaves, however, are more like 

 0. lata than 0. Lamarckiana. Whether 

 the only primary change, in the production 

 of 0. gigas, was the doubling of the num- 

 ber of chromosomes, from which resulted 

 the larger cells and hence the larger size 

 of the organs, or whether this is but a part 

 of the original change, can not be deter- 

 mined at the present time. 



Evidently all the mutants do not origin- 

 ate in the same way. 



0. lata X 0. gigas has 21 chromosomes 

 (one plant 20), and in reduction ten are 

 regularly segregated from eleven. Two 

 kinds of germ cells are thus produced. 

 Occasionally one chromosome passes to the 

 wrong pole of the spindle, making the re- 

 duced numbers nine and twelve. The 

 same irregularity in the germ cells occurs 

 in all the other hybrids examined, and, 

 more rarely, in several of the pure forms. 



The deviations of one or two from the nor- 

 mal somatic count, which have been ob- 

 served in several of the forms, are thus 

 simply and easily explained. 



Chromosomes of the 'Somatic Cells of the 

 (Enotheras: Miss Anne M. Ltjtz, Station 

 for Experimental Evolution. (By in- 

 vitation.) 



Root tips of pedigreed plants were used 

 exclusively for these studies and a number 

 of forms were reported upon at the Seventh 

 International Zoological Congress {Amer. 

 Nat., October, 1907). 



CEnothera lata (self-pollinated), 0. oh- 

 longa and 0. nanella had been only hastily 

 examined at the time of the first report, 

 but all have since been carefully studied. 

 The evidence for 0. lata is not conclusive ; 

 15 chromosomes have been counted, 14, and 

 also apparently 16. 



Of the three plants of 0. oilonga which 

 arose from Dr. D. T. MacDougal's self-" 

 pollinated 0. lata (original seed from Eng- 

 land), one showed 14 chromosomes and the 

 remaining two 15 each in every root tip 

 studied. 



Three plants of 0. nanella (seed from 

 Holland, pure bred about 15 generations) 

 gave 14 chromosomes each in A and B and 

 15 in C in every countable figure. 



Mr. R. R. Gates has reported the sporo- 

 phyte number of chromosomes for plants 

 said to be lamarckiana arising from a cross 

 between 0. lata 5 and 0. lamarckiana c? 

 to be about 20 (Science, February 15, 

 1907; Boi^. Gaz., February and July, 1907). 

 Of the seven offspring of a similar cross 

 which were identified as 0. lamarckiana, 

 I have found each plant to have 14 chromo- 

 somes in the cells of the root tips. Two 

 seedlings of 0. alhida arising from this 

 cross had each 15. 



Effects of Exposing Germ Cells to the Bays 

 of Radium: Dr. C. S. Gager, New York 

 Botanical Garden. 



