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CHAPTER XIII.
SYSTEMATIC AEEAHGBMENT.
T h i s has already been slightly sketched out, and the details
may he reserved for the characters which follow of the genera
of Fungi which occur in Great Britain, and the divisions under
which they are arranged. I t is impossible here to discuss the
various arrangements which have been proposed. The one
adopted is that which was given in Dr. Findley’s ‘Vegetable
Kingdom,’ and which, as regards the principal groups, is almost
identical with that of Fries. I t may be objected that it rests
on a single character, hut in spite of this objection, I know
of no arrangement which gives the true affinities of Fungi
better, and if it be recollected that it is impossible to arrange
any quantity of natural productions in a straight line so as to
exhibit their relations, but that these may be illustrated rather
by groups ranged round a common centre, bearing relations
to the several groups which surround them, it will he seen, I
think, that the arrangement does place together those species
which are closely allied, though connected also with others in
a contiguous group. Thus the Uredines pass through Podisoma
into the Tremellinæ, and Botrytis, or Sporotrichum, through
Isaria to Clavati. When the sporidia in an ascus are reduced
to one, and the sac fits closely to the sporidium, the body so
SYSTEMAT IC A R RA N G EM EN T . 87
formed is scarcely distinguishable from a spore, and we may
then have a passage from the ascigerous Fungi to the sporiferous.
I t is thus that we have sometimes the two forms of fruit in the
same hymenium, as in Tympanis (Plate 1, fig. 13).
I do not enter into the question of the affinities of Fungi
with other groups, because it supposes a knowledge of those
groups. 1 must refer, therefore, to what is said upon the
subject in the ‘ Introduction to Cryptogamie Botany.’
As regards the affinities which exist between one group and
another, we must take care that species are not placed together
merely from similarity of external form. Nothing can be more
close, for instance, than the external resemblance between a
simple Clavaria and a Geoglossum (Plate 23, fig. 33), and yet
no Fungi are more essentially distinct. So long as the true
structure of the hymenium in the higher Fungi was unknown,
they might be associated, but to associate them now would he
to substitute analogy for affinity. Again, under similar circumstances,
a Psilopezia and Corticium might be placed in the
same genus, hut the asci of the former indicate its alliance with
Peziza, and not with Auricularini. On the contrary, the relation
of Hysterangium to Phallus, though apparently so distant
when the latter is expanded, is most evident if the young plant
in the egg state be examined. And in the same way the relations
of Tremellini to Uredines are clear, if the large, often
lobed or septate cells from which the long threads which hear
the spores are developed, be compared with the primary spores
of Podisoma, while it is remembered that these spores give
rise to little buds, whatever he their nature, from their sides,
which are at the very least analogous with the tertiary spores
of some Uredinece. The transition from Tremella to Thelephora
through such species as T. sebacea (Plate 17, fig. 6) is
almost perfect.