THE WHITE RUST, ETC. 
477 
microscope reveals upon this fragment of grass-leaf. Little 
bundles of delicate threads, clear and crystalline, arc seated 
upon a branching slender mycelium. These threads, some- 
times erect, sometimes drooping, flexuous, or prostrate, are 
composed of numerous roundish or spherical cells attached to 
each other in a moniliform or bead-like manner (fig. 21). 
These easily separate from each other. Let a portion of the 
threads be removed from the leaf on the point of a lancet and 
laid upon a glass slide, with a thin cover over them. Submit 
this object to a quarter- inch power as a drop of water is let 
fall at the edge of the cover and insinuates itself, by capillary 
attraction, between the two plates of glass. So soon as it 
touches the moniliform threads the disunion commences, and 
almost before they are enveloped in the fluid Wo spherules 
will scarcely remain attached to each other. This delicate little 
mould on the grass leaf at one time bore the name of Oidium 
monilioides. It is now regarded only as a condition of another 
minute fungus, to which attention will shortly be directed. 
The vine disease so fearfully destructive on the Continent, 
and not altogether unknown in this country, is another of 
these incomplete fungi. From the individual who first dis- 
covered it in the South of England, it was called Oidium Tuclceri, 
which name it continued to bear, both here and abroad, until 
with many others, probably nearly all, of the same genus it was 
found to be only a barren state of, what is called by mycologists, 
an Erysiphe . If, towards the autumn, we should again collect 
some whitened, mouldy, or mildewed grass-leaves, similar in 
appearance to those mentioned above, and carefully look at 
them with a pocket lens, little black points, almost as small as 
a pin's point, or more resembling the full stop with which this 
sentence closes, will be found scattered over the white threads. 
The aid of the microscope must be again sought to make out 
the structure of the little black dots. Closely nestling upon 
the mycelium, the little points will prove to be spherical, 
brownish conceptacles, surrounded with transparent floccose 
appendages. Many other species are far more beautiful than 
that of the grass leaf, as will be seen by reference to our plate. 
The variation consists chiefly in the form of the appendages 
which spring from the conceptacle and surround it in a radiating 
(as in figs. 4, 7, 10, and 15), or in a more or less confused and 
entangled manner (as in figs. 1, 23, and 25). The surface of the 
conceptacle is minutely reticulated, and its base is attached to 
the mycelium. When first formed, these globose conceptacles 
are almost colourless ; they afterwards acquire a yellow colour, 
and are ultimately of a deep brown. The appendages are seldom 
at all coloured. Within the conceptacle are contained from one to 
several transparent obovoid sacs, or spore-cases called sporangia, 
VOL. in. — no. xti. 2 K 
