522 
R. RUGGLES GATES 
otherwise modified by crossing, the nature of the character and the 
possibihty of its modification through hybridization can never be 
wholly neglected. In certain cases this feature of change in the 
character becomes of great importance, overshadowing the mechanisrn 
by which the fundament of the character is transmitted. I am, of 
course, speaking here of permanent modifications in a character, and 
not merely of the temporary effects which may be produced in a 
heterozygous organism through the presence of other factors. 
When we study the nature of mutations which are fundamentally 
morphological it first becomes evident that each mutation is essentially 
a cell change, transmitted as such to every cell of the organism through 
mitosis. Before considering this aspect of mutation let us classify 
some of the known types of morphological mutations. For this 
purpose we will consider chiefly the genus Oenothera where these 
types of change have been most fully studied. It seems clear that all 
or nearly all the changes to which I refer have originally taken place 
in the nucleus of the cell. 
Referring first to chromosome changes, in the genus Oenothera the 
original number of chromosomes is 14. This is true of Oe. Lamar ckiana 
and many other species. Duplication of one of these chromosomes 
through an irregular meiotic division has led to 15 in Oe. lata, a charac- 
teristic mutation which has occurred both in Oe. Lamarckiana and in 
certain races of Oe. biennis. The same chromosome number occurs in 
semilata and in a very different form from Sweden which I have 
called incurvata.'^ DeVries^ has recently described still another form 
having 15 chromosomes. It was derived from Oe. biennis semigigas 
pollinated in part from Oe. biennis, and has flat leaves, whitish foHage, 
white veins, longer spikes, slender buds, small, erect flowers, thin 
cylindrical fruits and few seeds. Hence we may say that whenever a 
germ cell having 8 chromosomes fertilizes a normal germ cell a new 
form is produced, though what its characters will be depends upon 
various circumstances which need not be considered here. One of the 
most important of these factors is probably the particular combination 
of chromosomes received. It is perhaps not inappropriate to speak of 
all these mutants as belonging to the lata series, or the series with an 
extra chromosome. 
Oe. mut. gigas is the prototype of another series of still more 
2 Op. cit., p. 147. 
^ DeVries, Hugo. 1915. The coefficient of mutation in Oenothera biennis L. 
Bot. Gaz. 59: 169-196. 
