STRUCTURE. 47 
already-mentioned oval hilums are left behind. Naturally, the 
stem becomes longer by every perfoliation; in luxuriant speci- 
mens the length can reach that of some lines. Its partition is 
already, by the ripening of the first panicle from the beginning 
of its foundation, strong and brown; it is only colourless at the 
end which is extending, and in all new formations. During all 
these changes the filament remains either unbranched, except 
as regards the transient panicles, or it sends out here and there, 
at the perfoliated spots, especially from the lower ones, one 
or two strong branches, standing opposite one another and 
resembling the principal stem. 
The mycelium, which grows so exuberantly in the leaf, often 
brings forth many other productions, which are called selerotia, 
and are, according to their nature, a thick bulbous tissue of 
mycelium filaments. Their formation begins with the profuse 
ramification of the mycelium threads in some place or other; 
generally, but not always, in the veins of the leaf; the inter- 
twining twigs form an uninterrupted cavity, in which is often 
enclosed the shrivelling tissue of the leaf. The whole body 
swells to a greater thickness than that of the leaf, and protrudes 
on the surface like a thickened spot. Its form varies from 
circular to fusiform; its size is also very unequal, ranging 
between a few lines and about half a millimetre in its largest 
diameter. At first it is colourless, but afterwards its outer 
layers of cells become round, of a brown or black colour, and it 
is surrounded by a black rind, consisting of round cells, which 
separate it from the neighbouring tissue. The tissue withia the 
rind remains colourless ; it is an entangled uninterrupted tissue 
of fungus filaments, which gradually obtain very solid, hard, 
cartilaginous coats. The sclerotium, which ripens as the rind 
becomes black, loosens itself easily ‘from the place of its forma- 
tion, and remains preserved after the latter is decayed. 
The sclerotia are, here as in many other fungi, biennial 
organs, designed to begin a new vegetation after a state of 
apparent quietude, and to send forth special fruit-bearers. They 
may in this respect be compared to the bulbs and perennial 
roots of under shrubs. The usual time for the development of 
