242 SECRETS OF ANIMAL LIFE 
potentially before, during, or after fertilization. 
In short, there is nothing hard and fast about 
the origin or nature of mutations: their common 
features are their brusque appearance, their dis- 
continuity with the parent stock, and their capa- 
bility of being transmitted intact to a certain 
proportion of the offspring. This brings us to notice 
the recent masterly work of Dr. Ruggles Gates, who 
has been for many years a persistent investigator 
of the mutations of CEnothera. In his Mutation 
Factor in Evolution (Macmillan, 1915) he expounds 
the notable advance which his researches have 
secured. He has been able to show in circumstan- 
tial detail that the peculiarities marking the various 
mutants are correlated with observable alterations 
in the organization of the fertilized egg-cell, especi- 
ally as regards the nuclear rodlets or chromosomes 
of which each kind of organism has a definite num- 
ber. The fundamental number of chromosomes for 
the genus CEnothera is 14; this has become 15 in lata 
and semilata, 21 in semigigas, 28 in gigas, and so on. 
This change is observable in the fertilized egg-cell 
and is echoed throughout the whole plant. In this 
connection a reference may be permitted to what 
obtains in man. Competent observers have stated 
that the cells of the male negro have 22 chromo- 
somes, and it is probable that the negress has, at 
least in some cases, 24. Now in the case of the white 
man and woman the enumerations of chromosomes 
by very careful observers point to the numbers 
47 and 48 respectively. It seems to be very difficult 
