22 British Uvedinee and Ustilaginee. 
A section through one of them shows it to consist of an 
external envelope of cells, which encloses the body on all 
sides, above, below, and laterally. The base of the body 
is a circular disc (hymenium), which bears upon its upper 
surface a number of closely packed, erect hyphze (basidia), 
each of which supports a linear series of spores. The 
hymenium increases in width as the ezcidium develops, 
but whether from new basidia arising between those at 
first formed, or circumferentially, is not known. Sur- 
rounding the circumference of the hymenium is a circle of 
sterile cells (the peridial cells; Plate II. Fig. 2). Spore- 
formation in the ecidium proceeds from above downwards, 
in the following manner. The cells destined to become 
spores are enclosed in a hyaline tube (the mother-cell) ; 
they are at first colourless, but‘soon within each, from above 
downwards, a number of granules appear, which, becoming 
invested with a delicate membrane, rapidly augment in 
size, from an increase of the enclosed protoplasm, until they 
touch the walls of the mother-cell. ‘he granular contents 
are by this time orange (cidium), or brown (Restelia), 
or remain white in a few species, such as Ac. rumicis, 
vince, etc.* 
The growth of the cell continues until it is indistinguish- 
able from the mother-cell. By the mutual pressure of the 
neighbouring cells the young spores become polygonal. 
As this process begins above and continues downwards, or, 
as it is now termed, in a basipetal manner, it follows that 
the ripe spores are uppermost. As soon as they have 
attained their full maturity, they separate from one another 
and are blown away. In some species (Restelia, xcidio- 
* Mr. G. Massee considers the whole A®cidium to be a sexual product 
resulting from the conjugation of two dilated mycelial hyphee in the tissues 
of the host-plant (Annals of Botany, June, 1888, vol. ii. Pp. 47-51, plate iv. 
figs. 1-7). 
