276 
THE STUDY OF A LICHEN FROM OBAN. 
of the apotliecium, causing the ascus to be ruptured and the 
spores to be forced up to the surface of the disc. A remark¬ 
able feature of the apotliecium is that it produces a succession 
of asci, so that young ones are growing up to take the places 
of the old ones. 
The spermogones, a section of one of which is seen at s 
(Fig. 9), are flask-shaped receptacles formed in the medullary 
layer, but forcing for themselves a passage through the upper 
layers to the surface of the thallus and there opening by a 
minute pore. These receptacles contain a vast number of 
sterigmata, which give rise to the spermatia; the latter are 
easily detached by a slight pressure and rise through the pore 
to the surface. These spermatia are supposed by some to 
be used in the fertilisation of the plant, somewhat similar to 
the pollen grains in flowering plants, but this has never been 
proved to be the case. 
There is one other point to which we wish to draw 
attention ; it is the soredia, consisting of a granular powder 
which appears on the surface of the thallus, and is presumed 
to be the outgrowth of the gonidial layer. In some Lichens 
it forms oval patches scattered over the surface—as in 
Bamalina; in others it is developed on the edges, forming a 
border, as in Sticta scrobiculata; while in others it covers the 
whole surface—as in Pertusaria; and again, in other kinds it 
forms a coral-like (isidiose) appearance—as in Parmelia 
Saxatilis, var. furfuracea. 
In the specimen before us it does not assume any of these 
forms, but causes an abnormal growth of the thallus, which 
under the microscope looks like the rugged trunk and 
branches of an oak-tree, covered with an olive-green powder. 
And these clusters of branches (glomeruli) gave the old 
name to the plant Parmelia glomerulifera . They will be seen 
in Fig. 1, and in section in Fig. 9. 
The use of the soredia is generally supposed to be to 
perpetuate the plant when its surrounding conditions are 
unfavourable for the formation of spores. As for instance, 
Parmelia jjhysodes, which grows so abundantly on the Lickey 
Hills, and yet has never been found in fruit there : the plant 
may yet be found abundantly in every size, from some inches 
in diameter down to the germ just beginning life on its own 
account. Now this plant must depend upon the soredia only 
for its abundant and successful growth there in the general 
struggle for existence. 
From our study of this “Lichen from Oban” we may 
fairly conclude that loveliness and beauty are to be found 
in these lower forms of plant life as much as in those more 
