198 Macfarlanc — Cii7'rent 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 v.^ork, 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 



