l88 STRUCTURE AND LIFE HISTORIES 
commonly regarded as inheritance, but only a little 
careful thinking will lead us to see that resemblance 
and inheritance are by no means synonymous. The real 
nature of inheritance is well illustrated by the inheritance 
of property by a son from his father. The thing inherited 
is not an external appearance, but a material substance 
(land, buildings, a business), which is handed from one 
to another. So it is in reproduction. That which one 
generation of plants inherits from another is the substance 
of the reproductive cells the protoplasm of the spore, 
oosperm, tuber, or bulb plus a certain characteristic 
organization of this protoplasm, and the effects of its past 
history. 
170. Inheritance Versus Expression. That inheritance 
and expression are not the same thing is plainly shown in 
the life history of the fern, for the gametophyte clearly 
derives its living matter by inheritance from the sporo- 
phyte, and the sporophyte, in turn, its living matter from 
the gametophyte, and yet the two generations look so 
little alike that men for centuries knew them both with- 
out recognizing the fact that they were merely two dif- 
ferent phases in the life history of the same species of 
plant. So, often, among human beings, children may 
bear very little if any resemblance to their parents, but 
may closely resemble their grandparents. Clearly we 
do not inherit the color of our eyes or hair, the shapes of 
our noses, the peculiarities of our voices, or our mental 
traits from our parents, nor even from our more remote 
ancestors. What we do inherit is a tiny particle of proto- 
plasm having a certain characteristic composition, struc- 
ture, and past history. This protoplasm is capable, under 
certain combinations of circumstances, of developing 
