MEETING OF THE BRITISH ASSOCIATION. 29 
help of natural selection and variation, explain very many of the most 
obscure and interesting phenomena that oceanic island floras present. 
For instance, we may thus explain the persistence of ancient types in 
the islands that had succumbed in the struggle for existence on the 
continents ; the representation of continental genera and species by 
similar, but not identical, genera and species in the several islets of 
each group ; the graduated series of forms ascending from varieties to 
genera that islands often present, and the absence of such sharp lines 
of distinction between them as prevail in continental floras ; the ab- 
sence of whole continental orders on islands ; the fact of species being 
few in proportion to genera, and genera in proportion to orders, as 
compared with continental floras ; the tendency in many genera to 
assume grotesque and arborescent forms, etc. 
In concluding, the lecturer wound up as follows : — " And if so many 
of the phenomena of oceanic island floras are thus well explained by 
the theory of the derivative origin of species, and not at all by any 
other theory, surelv this is a strong corroboration of that theory. De- 
pend upom it, the slow but steady struggle for existence is taking ad- 
vantage of every change of form and every change of circumstance to 
which plants, no less than animals, are exposed ; and, that variation 
and changing of form is the rule in organic life is as certain as that 
definite combinations and mathematical proportions are the rule in the 
inorganic. By a wise ordinance it is ruled, that amongst living beings 
like shall never produce its exact like; that as no two circumstances 
in time or place are absolutely synchronous, or equal, or similar, so 
shall no two beings be born alike; that a variety in the environing 
conditions in which the progeny of a living being may be placed, shall 
be met by variety in the progeny itself. A wise ordinance it is, that 
ensures the succession of living beings, not by multiplying absolutely, 
identical forms, but by varying them, so that the right form may fill 
its right place in nature's ever-varying economy. 
"The acceptation of general principles, whether in the physical or 
biological sciences, has always been a slow process ; and I look for no 
exception in the case of the derivative origin of species. The physical 
sciences, however, have in this matter the start of the biological : 
scientific progress in them having commenced several centuries ago, 
whereas it is hardly one century since botany and geology first became 
the subject of exact and scientific study. Before that time not a system 
