The Stature and Chromosomes of Ocnothera gigas, De Vlies. 549 
will apparently accoimt for all the differences between 0. gigas aud 
0. Lamarckiana. There is no evidence of the presence of new or 
additional unit characters in 0. gigas, but tbe duplication in tbe set 
of chromosomes may be the only primary change. 
5. It is considered that the facts strongly Support the view of 
the independence and genetic coutinuity of the chromosomes in 
Oeuothera from geueration to generation, whatever may he their röle 
in heredity. They also indicate the correctness of Boveri’s view that 
chromosome number and not merely chromatin mass, is a factor in 
determining the size of cells. 
6. Examination of the evidence in otlier cases shows that a 
doubling in the number of chromosomes in a cell may or may not 
be accompanied by an increase in nuclear and cell size. Where 
there is no such increase this implies an accompanying internal or 
physiological readjustment. This makes it more probable that the 
primary change in the case of 0. gigas was a duplication in the 
set of chromosomes. 
7. It is considered most likely that the double number of chro- 
mosomes in 0. gigas originated soon after fertilization, by the fail- 
ure of a nucleus to complete its division after the chromosomes had 
divided, a condition comparable to the monasters of Boveri. 
8. There are various instances among plants, of closely related 
species one of which has twice as many chromosomes as the other. 
Some of these have probably originated in a manner analogous to 
the origin of 0. gigas from 0. Lamarckiana. This cannot be a com- 
mon method of species formation, however, and bears no necessary 
relation to the general processes of evolution in the group. It 
appears to be rather of the nature of an incident among evolutionary 
phenomena. 
Literature cited, 
Boveri, Tii. 1904. Ergebnisse über die Konstitution der chromatischen Sub- 
stanz des Zellkerns. Jena. 130 S. 75 Fig. 
1905. Zellenstudien V. Über die Abhängigkeit der Kerngröße und Zeilen- 
zahl der Seeigellarven von der Chromosomenzahl der Ausgangszeilen. 
Jena. 80 S. 2 Taf. 7 Fig. 
De Yries, Hugo. 1901. Die Mutationstheorie. Leipzig. Bd. I. 
1903. Bd. II. 
Erdmann, Rh. 1908. Experimentelle Untersuchung der Massenverhältnisse von 
Plasma, Kern und Chromosomen in dem sich entwickelnden Seeigelei. 
Arch. f. Zellforschung 2. 
