524 
R. RUGGLES GATES 
in any genus. Some of these "cleavage lines" are structural, some 
chemical in nature. 
Another important feature of mutations which has not hitherto 
been emphasized is the fact that each is the result of a cell change 
which is represented in every part of the organism. This change 
originally occurred in the nucleus of a single cell, and the mitotic 
mechanism is responsible for handing it down to every part of the 
organism. The cells of Oe. lata constantly have 15 chromosomes, in 
whatever part of the plant they have been examined. Similarly in 
Oe. gigas even the most specialized tissues retain the double number 
of chromOvSomes transmitted to them,^ though in the tapetal cells of 
all the forms secondary changes may take place, through fusion of 
nuclei and similar causes. 
The conclusion follows that, with non-significant exceptions, every 
cell receives the number of chromosomes transmitted to it from the 
original fertilized egg. The blunt-pointed, deeply crinkled leaves, 
short stature, irregular branching, nearly sterile pollen, rounded buds 
and other features of Oe. lata are then an external expression of the 
fact that an extra chromosome is present in every cell. The real 
mutation was a cell change and is transmitted by mitosis as a cell 
change. Although we have at present practically no knowledge of the 
relation between cell structure and external form in organisms, yet 
we can at least affirm that the original change from a 14- to a particular 
15-chromosome complex has resulted in the various external differ- 
ences which we observe between lata and Lamar ckiana. The organism 
is different because its every cell is different, and if in any part the 
extra chromosome should be dropped out into the cytoplasm through a 
slip in mitosis we should expect in that part a reversion to the foliage 
and other characters of Lamar ckiana. 
Viewed in this way, it is clear that we must consider the peculiar- 
ities of lata a result and not merely an accompaniment of the presence 
of the extra chromosome. We must, moreover, visualize the change 
as a cell change and the special features of lata as its external expression. 
The same point of view applies probably to all other mutants. 
This makes comprehensible the fact that in many cases the mutants 
differ from the parent as strikingly in the early seedling stages as in 
the mature plant. The ontogeny of the new form does not witness a 
^ These and similar facts point to the conclusion that the chromosome divisions 
during ontogeny are not differential in nature, as Weismann supposed, but equational. 
