The Stature and Chromosomes of Oenothera gigas, De Vries. 547 
be developed witli 64 chromosomes, because it is a return to the 
original 2 x number. It would be interestiug to make comparative 
measurements of cell size in some of these forms with 4 x chromo- 
somes, as well as to compare the statures of the adult plants. This 
would doubtless aid in analyzing their relationsliip. 
The fact that apogamy is so frequently associated with the 4 x 
number of chromosomes in a species, suggests some causal relation 
between the two facts. It is not impossible that 0. gigas itself may 
develope signs of apogamy. 
V. Evolutionary Status. 
It is probable that species have originated in nature from time 
to time by a doubling in the chromosome number, such as has occur- 
red in the case of 0. gigas. It is not likely however that this has 
been a common occurrence. Eather is it more of the nature of an 
accident, or rather, an iucident, among evolutionary phenomena. This 
emphasizes the necessity of distinguishing between species-origin and 
evolution, two things which are frequently held to be svnonomous. 
It is not evident that the origin of a particular new form in a par- 
ticular mauner has any necessary bearing on the general processes 
or trends of evolution in the group to which it belongs. In some 
groups of orgauisms, such as the Gymnosperms, the chromosome 
number (24) remains constant practically throughout the group, while 
in such groups as the Insecta and certain genera of Dicotyledons, 
some of which have already been cited, the number varies greatly 
within a single genus. This shows that species-formation, and evo- 
lution may go on for long periods without the chromosome number 
being affected, while the condition in the Insects would rather indi- 
cate a great amount of chromosome change in some not remote period. 
The doubling of the chromosome number in 0. gigas is 
to be looked upon merely as a duplication of the chromo- 
some set already present in 0. Lamarckiana. There is no evi- 
dence that any new uuit characters have been added or that any 
thing really new *) has come into the germ plasm. The sudden 
doubling, however it happened, led to numerous readjustments during 
ontogeny, and it is not certain that there is any difference between 
gigas and Lamarckiana which cannot be explained on this basis * 2 ). 
b In the sense of being additional. 
2 ) The possibility nnist. however, be recognized, that other changes took 
place at the same time as the doubling of the chromosomes. 
