246 LICHENS. 
have fallen down into the valley beneath, one can only explain the phenomenon by 
supposing that the algal and fungal cells concerned have been blown together, and 
that the opportunity has been afforded them on the blocks of stone of contracting 
a union. Now, so far as regards one of the two partners, viz.: the one devoid of 
chlorophyll, and known as a fungus—the idea that everywhere in the air spores of 
fungi are swarming about is so familiar to us that the supposition of an occasional 
stranding of individual spores, which are being blown about by the wind, upon the 
moist broken surfaces of stones can encounter no opposition. Respecting those 
spores in particular which are ejected from the aérial fructifications of lichens, the 
discussion of their life-history and distribution must of course be reserved for a 
later section; but it is necessary to make here the one statement that provision 
exists for the most profuse and distant dissemination of these spores. 
Thus, in the case of one of the partners, there is no difficulty in realizing its 
ubiquity. But when one comes to the Algz, the name at first calls up to mind the 
green filaments which oceupy our pools and ponds, or the brown wracks and red 
Floridez of the sea-shore, and we ask ourselves how it can be possible for these 
plants to occur on fractured surfaces of stone, especially on the débris of mountain 
sides. Indeed, it is certainly not Alg® of these kinds that take part in the 
construction of Lichens. The name Alge is properly only a general name for all 
Thallophytes containing chlorophyll, and it is applied to many small organisms 
besides those mentioned above, namely, to numbers of Nostocinex, Scytonemez, 
Palmellaceze, Chroolepidez, and these are the kinds which fall in with the cells of 
fungi and form lichens in conjunction with them. Owing to their minute size, 
they are apt to escape observation, and, in general, only attract attention when 
myriads of them clothe the bark of trees, cliffs, stones, or earth. In these situations 
they need but little moisture, and it is not necessary for any of them to live under 
water like other alg®; they become desiccated without sustaining the slightest 
injury and make their appearance on the substratum occupied by them at the first 
stage of their development, as powdery coats, and, in this condition being extremely 
light, are liable to be blown away by a wind of moderate strength, and so 
distributed over mountain and valley. 
That this dissemination is not merely hypothetical but an actual fact has been 
susceptible of easy proof by the following experiment, made in a mountain-valley in 
the Tyrol. A plane surface covered with white filter-paper, which was kept moist, 
was exposed to a south wind; in the course of a few hours numerous particles, like 
dust, adhered to the paper, and amongst them cell-groups of Nostocinez and others 
of the above-mentioned alge occurred regularly, in addition to organic fragments 
of the most various kinds, such as pollen-grains and spores of all sorts of mosses 
and fungi. All these bodies were deposited in the little depressions on the sheet 
of paper, and in the same way they rest in the grooves, cavities, and cracks in the 
surfaces of stone, bark, and old wood-work, where they succeed in reaching a 
further development as soon as the requisite quantity of water is provided. Now, 
if at these places the little algal cell-groups meet with hyphe belonging to the 
