LIFE-HISTORY OF PENICILLIUM. 858 
In the next stage the sclerotium enlarges by the increase 
in size of the inner elements, the interstices between the sterile 
hyphee becoming obliterated. The increase of the carpogonium- 
hyphe now becomes difficult, and causes compression of 
the sterile hyphe. The next change is the formation of a 
tissue from the cells of the sterile hyphe. The carpo- 
gonium hyphe can now be distinguished only by their 
filamentous nature, as they run among the pseudoparenchy- 
matous tissue of the sclerotium. The cells of the pseudo- 
parenchyma vary in size from the first, those near the carpo- 
gonium-hyphe being smaller from the pressure of the 
growing carpogonium. 
As soon as the growth in size of the sterile cells ceases the 
walls begin to thicken and the sclerotium to ripen. ‘This 
occurs in from five to six days after their appearance, or in 
from twelve to fourteen days from the sowing of the spores. 
The thickening begins simultaneously in the sterile cells of 
the periphery of the sclerotium, and also internally in the 
carpogonium-hyphe. The thickening of the sterile walls is 
accompanied by a change of colour, the yellow tint marking 
distinctly the boundary of the sclerotium. The sclerotium 
now no longer takes up nourishment from the outside, the 
substance for the thickening of the walls being supplied by 
the cell-contents, which consist, at the beginning of ripen- 
ing, of almost homogeneous protoplasm. The thickening 
goes on for from six to eight days, and when completed the 
cells are nearly empty. The external white covering of myce- 
lial hyphe now ruptures, and the coloured sclerotium appears 
in view, with its rough, uneven surface. ‘The sclerotia 
(Plate XVII, fig. 4) vary much in size and form, and are 
either separate (fig. 4 a) or united in small groups (fig. 4 6) 
of from two to ten. Some of the sclerotia measure 0°870 mm. ; 
others are only from 0°165 to 0:230 mm. They are hard and 
firm, and cannot be easily crushed, and from the thickness 
of the cell-walls thin slices for microscopic examination 
can be easily cut. The carpogonium-hyphe are then seen 
to form a series of branches, which spread irregularly in all 
directions from the original carpogonium as a centre towards 
the periphery of the sclerotium, and end at different distances 
from the surface. 
Briefly to recapitulate, we notice the following facts :—The 
sclerotia are formed on the mycelium of the sexual stage of 
Penicillium. ‘They are products of a sexual process. ‘They 
contain the germ of the second generation, produced from 
the fertilised carpogonium, and this germ, up to a certain 
stage of its development, remains inactive, in the form 
