198 Macfarlane—Current Problems 
alike be overlooked by us, and yet prove potent agents during 
the life role of organisms. Much of the serum therapeutic 
treatment of animal diseases at the present day is based on 
such a view, for whether a diphtheritic antitoxin or an anti- 
venin, both seem to be substances whose chemical activities 
are called forth by the presence of an antagonistic compound 
that is injurious to living tissues. 
Accepting it that the higher plants have been evolved from 
simple types, it might be inferred from much of the current 
discussion that many important substances have been acquired 
during the process of evolution. To estimate the truth of 
this we might attempt to compare the stock in trade, so to 
speak, of unicellular plants as existing now, with that of the 
highest multicellular plants. We are immediately struck with 
the remarkable uniformity in both. Cellulose and mucilagin- 
ous walls that grow by apposition, the living constituents that 
are enclosed, the varieties of plastid appearing in the proto- 
plasm, the carbohydrates, amides, proteids and other food 
constituents, the numerous ferments admirably presented in 
Green’s recent work, the acids, alkaloids, pigments, and even 
crystals, are common property of both ends of the series. 
True, we do not find all of these located in any one species, 
but they may nevertheless be viewed as one common heritage 
throughout the entire plant scale. With our present imper- 
fect knowledge, it would be rash to dogmatize as to which of 
these some plant species has or has not the active or latent 
power of producing, when the appropriate stimulus is applied. 
If two related species or varieties agree in all points, except 
that one appears red, while the other is green, the red pig- 
ment might fairly be viewed as a new formation, while in 
reality it may have appeared in previous generations of the 
plant, and the latent machinery for its development may have 
persisted. Later I will refer to some striking cases of this 
kind which have come under my notice. In what then does 
