STRUCTURE. 47 



already-mentioned oval hilums are left behind. Naturally, the 

 stem becomes longer by every perforation ; 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 sclerotia, 

 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 within 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 



