THE PRESENT POSITION OF THE THEORY 
OF DESCENT, IN RELATION TO THE 
EARLY HISTORY OF PLANTS. 
ADDRESS TO SECTION K (BOTANY) BY 
D. H. SCOTT, LL.D., F.R.S., 
PRESIDENT OF THE SECTION. 
Ir has long been evident that all those ideas of evolution in which the 
older generation of naturalists grew up have been disturbed, or, indeed, 
transformed, since the re-discovery of Mendel’s work and the conse- 
quent development of the new science of Genetics. Not only is the 
‘omnipotence of Natural Selection’ gravely impugned, but variation 
itself, the foundation on which the Darwinian theory seemed to rest 
so securely, 1s now in question. 
The small variations, on which the Natural Selectionist relied so 
much, have proved, for the most part, to be merely fluctuations, oscil- 
lating about a mean, and therefore incapable of giving rise to perma- 
nent new types. ‘The well-established varieties of the Darwinian, such 
as the countless forms of Hrophila verna, are now interpreted as 
elementary species, no less stable than Linnean species, and of equally 
unknown origin. The mutations of De Vries, though still accepted at 
their face value by some biologists, are suspected by others of being 
nothing more than Mendelian segregates, the product of previous cross- 
ings; opinion on this subject is in a state of flux. In fact, it is clear 
that we know astonishingly little about variation. 
My friend Dr. Lotsy, indeed, proposes to dispense with variation 
altogether, and to find the true origin of species in Mendelian segrega- 
tion ; inheritable variability, he believes, does not exist ; new species, on 
his bold hypothesis, arise by crossing, and so, as he points out, we may 
have an evolution, though species remain constant. Thus everything 
apparently new depends on a re-combination of factors already present 
in the parents. ‘The cause of evolution lies in the interaction of two 
gametes of different constitution.’ 
I am aware that very surprising results have been obtained by 
crossing. Nothing could well have been more striking than the series 
of Antirrhinwm segregates which Dr. Lotsy showed us some years ago 
at a meeting of the Linnean Society. And now we hear of an apetalous 
Lychnis produced by the crossing of normally petaloid races. We do 
not know yet to what extent that sort of thing goes on in Nature, or 
what chance such segregates have of surviving. Still, if one may judge 
by Dr. Lotsy’s experimental results, ample material for Natural Selec- 
tion to work on might be provided in this way.? 
, 1 See Dr. Lotsy’s book, Hvolution by Means of: Hybridisation, The Hague, 
916. 
