K.—BOTANY. 247 
remunerative pursuit. ‘Their interest is in the process itself rather than 
in the phylogenetic connexions of its particular results. They want to 
know what brings about development and evolution, what are the 
driving forces behind these processes. 
The orthcdox ‘ Darwinian’ answer to this question, so far as it 
applies to phylogenesis, was ‘ natural selection.’ The organism was 
supposed to be capable of indefinite ‘ spontaneous ’ but heritable varia- 
tion in all directions and of various degrees, and those which happened 
to be useful to the organism by giving it a decisive advantage in the 
struggle for existence were preserved because the individuals which 
showed them alone survived and produced offspring, which inherited 
the useful variations and thus modified the species. ‘Two or more diver- 
gent sets of variations might happen to fit different individuals of a 
parent species to different sets of conditions, different habitats, into 
which they had wandered, while the parent species remained behind 
unmodified in the original habitat, and thus new varieties were supposed 
to originate. By the further development of the new characters, i.e. by 
the favouring of further variations in the same direction as the original 
ones, these varieties became distinct species. The same process further 
continued and involving also other structural features would lead to the 
wider divergence of the derivatives from the original stock, and this 
divergence would ultimately become so great that the different forms 
would be placed in distinct genera. The sharpness of the specific and 
generic distinctions would often be enhanced by the disappearance of 
the original or of intermediate forms, owing for instance to the physical 
conditions of life changing and becoming unsuitable for them or to 
their suppression by rivals whose variations had been more successful. 
In the course of a very long time, by a continuation of the same pro- 
cesses, the distinctions which were at first specific, and later generic, 
would become family distinctions, later again ordinal distinctions, and 
so on up to the great phyla. 
Alongside of the evolution of new species, genera, and families in 
the same general environment, such for instance as the tidal zone, there 
had been a migration of some forms to the land, or perhaps, as Mr. 
Church would have us suppose, a gradual raising of the land bearing 
aquatic forms above the water-level. These aquatic forms had thus 
been faced by conditions of life very different from the earlier ones, so 
that the variations which were preserved and perpetuated were necessarily 
in new directions. and gradually built up the equipment of the land plant 
—the typical leaf and root, the vascular and aerating systems, the 
cuticle, the air-distributed spores. From these earlier land plants again 
by further variation the heterosporous forms were derived, and finally 
the seed and angiospermy, while various progressive complications and 
modifications of the primitive vascular tissue, including secondary 
thickening, had established both more copious and more efficient con- 
ducting and mechanical systems, and thus led to the quickly growing, 
largely upright, modern plants, extraordinarily ‘ fiexible ’ to various life 
conditions. 
I think this is a fair rough statement of what was often known as 
the Neo-Darwinian account of evolution, as applied to plants, in the 
