a^]NOTlIEliA :\IUT. LATA AND (E. ]\1UT. SEMI LATA. 555 
The niuiierons types of meiotic iiTegularity described in 
this paper call for no remarks except to point out that not 
only may they lead, in the comparatively rare instances when 
such cells survive, to new numbers of chromosomes, but they 
might result in the perpetuation of half-chromosomes or 
fragments of chromatin in later cell generations. This, we 
believe, would be a source of external variability in the plants, 
and all such alterations in nuclear content should be looked 
upon as germinal changes. 
The Chromosomes in Ontogeny. — The statement is 
sometimes made that variations in chromosome number are of 
no greater significance than any other variations, and that in 
a lily, for example, deviation from 24 as the chromosome 
number is no more significant than fluctuation of the stamens 
around 6, the usual number. It is obvious, however, that a 
fundamental difference exists between the nuclear constitution 
of any organism, which is determined at the time the pro- 
nuclei unite in fertilisation, and the external characters of 
the organism, Avhich appear later. In other words, the 
chromosome content is practically the only visible structure 
Avhich is of primary significance, because it is transmitted as 
such from the previous generation, while all external 
features arise secondarily through the interaction of nucleus 
and cytoplasm as the organism develops. 
Finally, the lata and semi lata forms furnish in their 
origin a case of mutation par excellence, the essential 
germinal change occurring when a chromosome is distributed 
to the wrong germ nucleus. The germinal change constituted 
by this irregular or exceptional meiotic division leads to the 
development of an individual whose cells have a 15-chromo- 
some instead of a 14-chromosome content. The organism, 
therefore, develops along a uoav line of stability, though 
that stability cannot be fully maintained in the offspring, 
because in reduction there is an odd or unpaired chromosome. 
In the lata rubricalyx individual above described, the 
contrast between the usual processes of hybrid inheritance 
and the -exceptional changes constituting a mutation is 
