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441 MR. H. b. GUPPY : PLANT-DISTRIBUTION 
by the Podostemacez, Dr. Willis connects the dorsiventrality of these 
organs with that of the vegetative organs, thus introdueing a factor appa- 
rently subversive of all taxonomic principles. There is in his warning of 
the insecurity of the taxonomist’s position an echo of Huxley's defiant note 
respeeting the revolutionizing effect of the evolutionary doctrine on the 
principles of taxonomy and distribution. Dr. Willis wields the Podostemacerm, 
as Huxley wielded the Gentians, in his attack on prevailing principles. In 
the ease of Huxley it was concerned with the differentiation of a wide- 
ranging primitive family type, and one ean scarcely doubt that he struck a 
true note in his declaration. But it applied only to the second era, the era 
of differentiation, the age of influences still in operation, the age of normality, 
if we may so term it ; and it ought to havea profound effect on the methods 
of the taxonomist and on the prineiples of distribution. In the case of 
Dr. Willis it is concerned with the abnormal side of plant-life and does not 
really affect the validity of prevailing taxonomic principles. The difference 
is very significant, since, in view of the position taken at the commencement 
of this paper, we can in our day only look in that direction for a clue to the 
influence at work during the first era in the history of the Angiosperms, 
the age that witnessed the rise of the great families, the age of abnormalities, 
as it may be called. It is in this first era that the Mutation theory will find 
its appropriate field of investigation, and it is here that the principles 
disclosed by Dr. Willis in his prolonged investigations on the Podostemaceze 
wil apply. 
Before proceeding. to deal in the two following paragraphs with my 
interpretation of the lessons to be learned from the behaviour of the Podo- 
stemacee and with their application to the first era, I may say that 
Dr. Willis left room for an interpretation of the same kind, but was 
prevented, as he tells me, from entering a domain of pure surmise. 
Postulating for terrestrial] plants an era when uniformity in environment 
was the rule—an era, one might imagine, of. great atmospheric humidity, 
when persistent cloud-coverings blanketed the globe and when the same 
equable temperature everywhere prevailed,—the writer pictured a plant- 
organism under such conditions as behaving very much like a ship in a 
calm, drifting in a morphological sense in all directions and displaying 
unchecked and irresponsive variations of the floral organs of a kind very 
disquieting to the taxonomist and all non-adaptive in their nature. He 
came to see that such modifications would become more and more fixed as 
the differentiation of conditions proceeded, the degree of mutability varying 
inversely with the diversification of environment. 
Stated in the language of the mutationist, this would imply that the 
mutations of the floral organs of our own day represent all that remains of 
the capacity for great morphological changes in the early ages of the history 
of the Angiosperms. A mutation as at present recognized is non-adaptive. 
