d of the surrounding conditions, as well
as through the inter-crossing of distinct individuals, but not through
natural selection; for as these morphological characters do not affect
the welfare of the species, any slight deviations in them could not have
been governed or accumulated through this latter agency." (Ibid. page
176.)

This is a sufficiently liberal concession; Nageli, however, went much
further when he said: "I do not know among plants a morphological
modification which can be explained on utilitarian principles." (See
"More Letters", Vol. II. page 375 (footnote).) If this were true the
field of Natural Selection would be so seriously restricted, as to leave
the theory only a very limited importance.

It can be shown, as the writer believes, that many typical
"morphological characters," on which the distinction between great
classes of plants is based, were adaptive in origin, and even that their
constancy is due to their functional importance. Only one or two cases
will be mentioned, where the fossil evidence affects the question.

The pollen-tube is one of the most important morphological characters of
the Spermophyta as now existing--in fact the name Siphonogama is used
by Engler in his classification, as expressing a peculiarly constant
character of the Seed-plants. Yet the pollen-tube is a manifest
adaptation, following on the adoption of the seed-habit, and serving
first to bring the spermatozoids with greater precision to their
goal, and ultimately to relieve them of the necessity for independent
movement. The pollen-tube is constant because it has proved to be
indispensable.

In the Palaeozoic Seed-plants there are a number of instances in which
the pollen-grains, contained in the pollen-chamber of a seed, are so
beautifully preserved that the presence of a group of cells within the
grain can be demonstrated; sometimes we can even see how the cell-walls
broke down to emit the sperms, and quite lately it is said that the
sperms themselves have been recognised. (F.W. Oliver, "On Physostoma
elegans, an archaic type of seed from the Palaeozoic Rocks", "Annals of
Botany", January, 1909. See also the earlier papers there cited.) In
no case, however, is there as yet any satisfactory evidence for
the formation of a pollen-tube; it is probable that in these early
Seed-plants the pollen-grains remained at about the evolutionary level
of the microspores in Pilularia or Selaginella, and discharged their
sp