122 MISS S. LONGMAN ON THE DRY-ROT OF POTATOES. 
iransverse wall or none. Since, however, all transitions from aseptate to 
7-septate forms occur, the aseptate spores cannot be considered to belong to 
a type distinct from those with septa (see Pl. 10, A). 
On potatoes attacked by dry-rot two types of pustules are frequently pro- 
duced. The simplest consists merely of small tufts of hyphæ bearing typical 
Fusarium spores, and these pustules, though sometimes pink, are usually 
white or buff-coloured. In the second type the spores are enclosed in a thin 
wall of closely-interwoven hyphæ. The pustule-wall is sometimes buff, but 
more often pink in colour (Pl. 10, D). 
The walls of some pustules have no opening, but others have a small 
circular orifice near the apex, and may thus be regarded as pycnidia. If a 
pustule of the latter kind is mounted in a drop of water, masses of the 
typical Fusarium spores are ejected through the circular opening at the apex 
of the pyenidium, and by their swelling, rupture its walls. 
As the pustules get older they lose their somewhat hemispherical and 
regular form, and give place ultimately to mere spore-bearing patches of 
mycelium. In some cases, before they have lost their shape the hyphæ at the 
base of such patches turn dark blue and become very closely interwoven, thus 
forming a hard, dry sclerotium. Meanwhile the upper part turns bright 
blue, and two different types of spore appear. 
The spores of the first type resemble the typical Fusarium spores in shape, 
but contain one or several round refractive bodies, situated either towards the 
end or in the middle of the spores (Pl. 10, В). 
The spores of the second type resemble somewhat the round bodies included 
in the spores of the first type, but are borne directly on the mycelium, either 
singly or in groups of two or three. In some cases the spores do not remain 
round, but become more or less pointed at the apex (PI. 10, C). 
The spores of the first type remain viable for years. Thus spores of a blue 
culture made in 1905 and allowed to dry up, grew freely when planted out 
in 1908, giving rise again to a blue culture. 
The period of viability of the blue Fusarium spores of Type II. has not 
been tested. 
The resting spores when dry are capable of resisting a fairly high 
temperature, withstanding 64:5? C. for 10 hours. When wet they are 
readily killed at 50? C. 
It has been seen that Fusarium Solani varies а great deal in form and 
colour. All the variations already described are to be met with in the fungus 
growing on living potato ; and with the exception of the pustules, which were 
only found breaking through the skin of potatoes, they occur also in cultures 
growing on sterilized potato. 
The different colours of the fungus therefore appear, like the different 
types of spores, to mark stages in its development rather than to be caused 
