CRYPTOGAMS. 
259 
cal or globose masses from 10 to 15 cm. in diameter, 
consisting of a whitish membrane becoming dark with 
age, and a brownish-black mass of spores which are 
nearly spherical and about 7 ;jl in diameter. Ustilago 
should be carefully dried and not kept longer than 
one year. It contains an alkaloid, secaline; sclerotic 
acid ; fixed oil about 3 per cent. ; and other substances 
as well. 
III. LICHENS. 
The Lichens include a group of plants, the individ- 
uals of which are composed of a fungus and an alga, 
which have a symbiotic relationship ; that is, one of 
mutual benefit. The fungus absorbs inorganic ma- 
terials from the substratum, and the alga manufac- 
tures the organic materials from carbon dioxide and 
water, the two plants thus being able to live on rocks 
and barren places where they could not otherwise live 
alone. 
The structure of the lichen embodies that of both 
the fungus and alga. The fungus consists of numerous 
branched hyphae, with transverse walls, forming a 
well differentiated outer and middle layer; and from 
that portion attached to the substratum, rhizoid-like 
filaments are developed. The Algae, which are asso- 
ciated with Fungi in this manner, belong to the 
simpler forms, consisting of a single cell or chain of 
cells, and may be situated either in distinct portions 
of the hypha, as between the middle and outer layers, 
or scattered throughout the tissues of the fungi. 
The organs of fructification are those of the fungi, 
chiefly of the Ascomycetes, and occur on the tliallus 
in the lichens as more or less circular, usually dark- 
colored spots; these constitute the ascocarps or apothe- 
cia and are characteristic for a number of medicinal 
barks, as rhamnus purshiana and granatum. 
