PRESIDENTIAL ADDRESS. 681 
proportion—of the individuals of the succeeding generations. Insuch an example, 
where both agents or primordia are present, one of them lies dormant, whilst the 
dominant one alone influences the course of metabolic processes, and thus brings 
about the appearance of the character itself. The dormant primordium can be 
transmitted as such through many generations, betraying its existence in each by the 
occurrence of some individuals in which it tindsits perfect expression. This happens 
when the opposite dominant agent or primordium has been removed from some 
of the gametes by the sorting-out process during the heterotype mitosis to which 
I have already alluded. 
The particulate character of inheritance seems, as many writers have pointed 
out, to demand a structural organisation for its basis ; and the units or primordia 
of which the latter is composed must be relatively permanent, inasmuch as 
heredity itself is so stable. The agents or primordia themselves probably act by 
definitely influencing the course of chemical reactions that proceed within the 
living protoplasm, somewhat after the fashion of the ferments. But whether this 
influence on the course of metabolism is to be attributed more directly to the 
chemical or the physical aspect of the organisation must, of course, remain an 
open question, though I incline to the latter alternative on grounds which I have 
already indicated. 
The processes of the higher metabolism offer suggestive analogies with those 
reactions for which the ferments are responsible. In contemplating them one can 
hardly fail to be struck by the orderly way in which ferment succeeds ferment on 
an appropriate medium. Each one produces its own special change, which it is 
unable to carry further itself, but it thereby provides a substratum suitable for its 
successor. Starting, for example, with a complex substance like cane sugar, we 
see it acted on by a series of ferments, each the result of protoplasmic differentia- 
tion, and each one carrying the process of disintegration a little further, but 
strictly limited in its power to act, and only able to take the change on to a 
definite stage. 
Everyone who has experimented with plants with the view of inducing the 
formation of some structure foreign to the species or individual by artificial 
means must have become impressed by the great difficulty of getting into touch, 
so to speak, with the higher metabolism at all. It is often easy enough to divert 
the life-history into either the vegetative or the reproductive channel, as every 
gardener is more or less consciously aware, and as Klebs has conclusively shown in 
his remarkble series of carefully conducted experiments. But even here it is some- 
times difficult to exactly hit off the conditions requisite to ensure the production 
of one or other of the various phases of the life-history. There are many furgi, 
for example, which are believed to represent vegetative stages of Ascomycetes or 
Basidiomycetes, but it has not yet been found possible to ascertain the conditions 
that would cause them to form the highest fructifications. Even in simpler 
instances a similar difficulty is sometimes encountered. Thus Bispora moniliforme, 
a mould that often occurs on the wood and stumps of oak or hornbeam, is not 
readily cultivated as the Bispora form, whether it be grown on wood or on various 
nutritive media. The usual result of raising it under artificial conditions is to 
obtain a luxuriant crop of Eurotium-like mould. But the Bispora form can be 
reproduced from such a culture by growing it in strong solutions of cane sugar 
under certain conditions, all of which are not as yet understood. 
I take it we shall agree that the properties of structure and form are to be 
interpreted as the necessary result of the action of particular substances on the 
protoplasm, and that these cause it to assume those definite attributes which we 
term specific on account of their constancy through a larger or smaller range of 
individuals. But this constancy of form must then be the result of a correspond- 
ing definiteness in tha series of changes undergone by the raw materials supplied 
as food in their upward transformations; each stage in the process limits the 
possible range of those that follow, as in the case of the ferments to which I have 
alluded ; and thus it becomes increasingly difficult to modify the final result. 
In this way we may see, perhaps, an explanation of the circumstance that in 
amphibious plants the particular structure, whether adapted for land or water, 
