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LICHEN GONIDIA 25
D. .THEORIES AS TO THE ORIGIN OF GONIDIA
Though the relationship between the gonidia within the thallus and free-
living algal organisms seemed to be proved beyond dispute, the manner in
which gonidia first originated had not yet been discovered. Bayrhoffer 1
attacked this problem in a study of foliose and other lichens. According
to his observations, certain colourless cells or filaments, belonging to the
"gonimic" layer, grew in a downward direction and formed at their tips a
faintly yellowish-green cell ; it gradually enlarged and was at length thrown
off as a free globose gonidium, which represented the female cell. Other
filaments from the "lower fibrous layer" of the thallus at the same time grew
upwards and from them were given off somewhat similar gonidia which
functioned as male cells. His observations and deductions, were fanciful,
but it must be remembered that the attachment between hypha and alga
in lichens is in many cases so close as to appear genetic, and also it often
happens that as the gonidium multiplies it becomes free from the hypha.
In his Meuioire sur les Lichens, Tulasne 2 described the colourless
filaments as being fungal in appearance. The green cells he recognized as
organs of nutrition, and once and again in his paper he states that they
arose directly by a sort of budding process from the medullary or cortical-
filaments, either laterally or at the apex. This apparently reasonable view
of their origin was confirmed by other writers on the subject: by Speer-
schneider 3 in his account of the anatomy of Usnea barbata, by de Bary 4
and by Schwendener 5 in their earlier writings. But even while de Bary
6
he noted
accepted the hyphal origin of the gonidia, that, accompanying
Opegrapha atra and other Graphideae, on the bark were to be found free
Chroolepus cells similar to the gonidia in the lichen thallus. He added that
gonidia of certain other lichens in no way differed from Protococcus cells;
and as for the gelatinous lichens he declared that "either they were the
perfect fruiting form of Nostocaceae and Chroococcaceae hitherto looked
on as algae or that these same Nostocaceae and Chroococcaceae are algbe
which take the form of Col/etna, Ephebe, etc., when attacked by an ascomy-
cetous fungus."
All these investigators, and other lichenologists such as Nylander 7
regarded the free-living organisms identified by them as similar to the green
cells of the thallus, as only lichen gonidia escaped from the matrix and
vegetating in an independent condition.
The old controversy has in recent years been unexpectedly reopened by
Elfving 8 who has sought again to prove the genetic origin of the green cells.
His method has been to examine a large series of lichens by making
sections of the growing areas, and he claims to have observed in every case
1
2 ;!
4
Bayrhoffer 1851. Tulasne 1852. Speerschneider 1854. de Bary 1866, p. 242.
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* 6
8 Schwendener 1860, p. 125. deBary 1866, p. 291. Nylander 1870. Elfving 1903 and 1913.
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still
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