ORIGIN OF SPECIES 517 
only a similar reference to the theory in following paragraphs, al- 
though my former paleontological work suggests a much wider 
application of it. 
The theory begins with a philosophical concept concerning the 
molecular constitution of the protoplasm of organisms, as set forth 
in the author’s treatise on intracellular pangenesis.* It assumes 
that the specific attributes of multicellular plants result from the 
special molecular constitution of their protoplasts, or cell contents ; 
and that these attributes are built up of sharply defined intracel- 
lular units, which normally combine in groups. This specific 
group-combination has much stability, but it is subject to change 
by sudden, independent action of some unknown determinate 
cause. That change is the initial step in mutation and consists of 
the addition, or substitution, of one or more units to an estab- 
lished group and the consequent rearrangement of the units of 
that group, forming a new one. 
Upon the integrity of the groups of units depends the stability 
of the specific attributes. Their normal tendency to stability is so 
great that initial group-changes do not occur in the somatoplasts 
of plants but only in the plasma of certain of their reproductive 
cells ; and they occur there only seldom. Ordinarily, when such 
a change occurs, it is only in the odplast of the germ cell of the 
ovule which is about to originate a new plant. If no change of 
Specific units occurs in the odplast the case is one of ordinary re- 
Production. If sucha change does occur in the odplast the case is 
- One of mutation as well as of reproduction, all the cells of the 
coming plant naturally partaking of the same specific attributes. 
It should be here remarked that such cases as the reputed or- 
igination of the nectarine from the peach are apparent exceptions 
to the rule just mentioned. That case being one of ordinary asex- 
ual reproduction and if it really was also a case of simultaneous 
Origination of a new species, initial mutative change must have 
©ccurred in the plasma of the apical cell of the mutating bud. If 
Mutation may occur in correlation with asexual reproduction, mu- 
tative molecular change in pollen cells would seem to be unneces- 
Sary in mutating cases of sexual reproduction. 
Gh ppc aa 
* See Intracellulare Pangenesis. Von Hugo de Vries. Pp. 212, Jena, 1889. 
