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BOTANY. 87 
found on iron, lead, etc., certainly not living at the expense 
of these metals, the distinction of the aerial nutrition of 
Lichens from the parasitical of Fungi evidently does not 
hold good in all cases. The presence of green spores is 
very constant, but their absence in forms like Alrothallus 
makes Lichens of this kind undistinguishable from Fungi. 
Lichens, as a rule, are aerial plants; yet some forms are 
always immersed in water,as in most Alge, The early 
stages of many Lichens resemble so closely certain Algae 
that botanists cannot separate them. The Lichens are 
considered by most naturalists as standing between the 
Alge and Fungi. According to Haeckel (* Natural History 
of Creation," p. 416), *each Lichen is composed essentially 
of two different plants, of a low form of Alga (Nostoc, 
Protococcus) (Fig. 111) and of a parasitic Fungus (Asco- 
mycetes) (Fig. 110), which is parasitic on the first, and lives 
off the assimilated material which this furnishes. The green 
chlorophyll-holding cells (gonidia), which one finds in every 
Lichen, belong to the Alga. The colorless threads (hyphi), 
on the contrary, which, thickly woven, form the principal 
mass of the body of the Lichen, belong to the parasitic 
Fungus. But always are both plant-forms—Fungus and 
Alga, which are considered as belonging to different classes 
—so firmly bound with one another, and so intimately 
grown together, that every one regards the Lichen as a 
single organism." 
Notwithstanding the differences in size, color, form, 
reproduction, and habitat seen in this brief survey, the 
structure of Algze, Fungi, and Lichens has always appeared 
to be the same, cellular. When we compare plants appar- 
ently so distinct as mushrooms, mildews, encrusting matter 
of rocks, greenish layers of ponds, sea-weed, etc., the 
closest examination rarely reveals more than a combination 
of cells, no Alga, Fungus, or Lichen offering us the dis- 
tinction of stem, leaves, vessels, or flowers observed in the 
