40 HEREDITY AND EVOLUTION IN PLANTS 



(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. 



30. Inheritance Versus Expression. — That inherit- 

 ance 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 

 sporophyte, 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 

 into a mature organism, resembling the one from which 

 it came, but under other combinations of circumstances 

 the external appearance — the expression — -may resemble 

 that of the parent only a very little, or not at all. In- 

 heritance may therefore he defined as the recurrence in 

 successive generations, of a similar cellular constitution.^ 



'Following Johannsen, Cf. p. 67. 



