579 
Heterosporium asperatum. By Mr. G. Massee. 
about 1*5-2 fju in diameter ; this mycelium, when produced on the 
surface of a suitable leaf, soon enters by way of a stoma into the 
interior. When once within the leaf, the mycelium at first forces its 
way between the cells of the host, the main branches soon acquiring 
a thickness of 8-10 p, and becoming transversely septate, the cells 
averaging 2-3 times as long as broad (fig. 9) ; by degrees the walls 
of the hyphae become tinged brown, and with age are dark brown and 
nearly opaque. The cells of the mycelium each contain one or 
more small, highly refractive, oleaginous globules, which disappear 
when treated with an alkaline solution. Thinner lateral branches are 
given off at intervals by the hyphae described above ; these at once 
pierce the wall of an adjacent cell, pass into the interior, and form a 
complicated coil (fig. 10) ; their function being that of assimilating 
food at the expense of the contents of the cell. These filamentous 
haustoria remain colourless, and contain granular protoplasm so long 
as their functional activity continues, but become brown like the 
parent hypha when the contents of the cell are exhausted. 
The main branches of mycelium run between the epidermal cells 
of the upper surface of the leaf, and the haustoria penetrate into the 
interior of the cells of this layer. Within a fortnight after first 
entering the leaf, the mycelium has usually radiated from the point 
of injection and formed a more or less circular patch about 1 cm. in 
diameter, and of a pale yellow colour ; this patch has now sunk below 
the ordinary surface-level of the leaf, owing to the collapse of the 
epidermal cells. In the meantime numerous short, lateral branches 
of the primary hyphse have developed a pseudoparenchymatous mass 
of tissue at the apex, the superficial cells of which give origin to the 
sporophores (fig. 9). The sporophores, owing to their mode of origin, 
are fasciculate, varying in number from four to ten, and sometimes 
emerge from the substance of the leaf through a stoma, at others by 
rupturing the epidermis. The sporophores, when fully developed, 
measure 120-150 p in length by 8-10 p in diameter, and are divided 
into 6-9 cells by transverse septa ; the basal cell, resting on the 
sclerotioid base, is inflated. The walls when matured are brown, 
becoming paler upwards. The terminal cell bears 2-4 very short, 
slender outgrowths, or sterigmata, that bear the spores. During the 
growth of the sporophores, the basal cells of the sclerotioid base send 
out colourless hyphae ; these penetrate the cells of the host for the 
purpose of obtaining food (fig. 9). 
The young spores are one-celled and furnished with a colourless, 
very thin epispore. As growth proceeds, a transverse median septum 
is formed, and at this stage the epispore becomes very slightly tinged 
with olive, and the minute external warts with which it is studded at 
maturity make their appearance. At a later stage two more trans- 
verse septa are formed simultaneously, one at each side of the first 
formed septum. In rare instances two additional septa are formed in 
2 b 2 
