PDF - CES (IISc)

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REPRODUCTION
possible: those who consider them to be sexual structures call them spermogonia
; those who refuse to accept that view write of them as pycnidia.
Tulasne, Nylander and others unhesitatingly accepted them as male
organs without any knowledge of the female cell or of any method of ferti-
lization. Stahl's discovery of the trichogyne seemed to settle the whole
question ; but though he had evidence of copulation between the spermatium
and the receptive cell or trichogyne he had no real record of any sexual
process.
Many modern lichenologists reject the view that they are sexual; they
regard them as secondary organs of fructification analogous to the pycnidia
so abundant in the related groups of fungi. One would naturally expect
these pycnidia to reappear in lichens, and it might be considered somewhat
arbitrary to classify pycnidia in Sphaeropsideae as asexual reproductive
organs, and then to regard the very similar structures in lichens as sexual
spermogonia. It has also been pointed out that when undoubted pycnidia
do occur on the lichen thallus, as in Calicium, Strigula, Peltigera, etc., they
in no way differ from structures regarded as spermogonia except in the size
of the pycnidiospores and, even among these, there are transition forms.
The different types of spermatia can be paralleled among the fungal pyc-
nidiospores and the same is also true as regards the sporophores generally.
Those described as arthrosterigmata by Nylander as endosporous by
Steiner were supposed to be peculiar to lichens; but recently Laubert 1 has
described a fungal pycnidium which grew on the trunk of an apple tree and
in which the spores are not borne on upright sporophores but are budded
off from the cells of the plectenchyma lining the pycnidium. It may be that
future research will discover other such instances, though that type of sporo-
phore is evidently of very rare occurrence among fungi.
b. COMPARISON WITH FUNGI. The most obvious spermogonia among
fungi with which to compare those of lichens occur in the Uredineae where
they are associated with the life-cycle of a large number of rust species.
They are small flask-shaped structures very much like the simpler forms of
pycnidia and they produce innumerable spermatia which are budded off from
the tips of simple spermatiophores. The mature spermatium has a delicate
cell-wall and contains a thin layer of cytoplasm with a dense nucleus which
occupies almost the whole cavity, cytological characters which, as Blackman 2
has pointed out, are characteristic of male cells and are not found in any
asexual reproductive spores. If we accept Istvanm's 3
description and figures
of the lichen spermatia as correct, their structure is wholly different : there
being a very small nucleus in the centre of the cell comparable in size with
those of the vegetative hyphae (Fig. 1 15).
1 Laubert 1911.
2 Blackman 1904.
3 Istvanffi 1895.