236 Transactions of the Royal Society of South Africa. 
General Characteristics. 
The mycelium may be persistent or evanescent ; in the latter case it is 
poorly developed, and disappears as soon as the thyriothecia are formed. 
The genus Asterina (2) may be taken as typical of the family ; in this 
genus the spore germinates at one or both poles, as a general rule sending 
out first a small papilla of limited growth which closely resembles in form 
the hyphopodia on the mycelium ; one or two germ tubes are subsequently 
developed from each pole, and these elongate, forming septate hyphae which 
branch alternately and produce hyphopodia at more or less regular intervals. 
The hyphopodia are extremely varied in form, and are of the greatest 
diagnostic value. Alternate branching is the rule, but in some species 
opposite branching is predominant. The mycelium develops centrifugally, 
and the mother spore can long be detected unaltered in the centre ; its per- 
sistent character is often useful in determining the nature of the epispore at 
maturity, when the spores in the ascus are more or less immature. In a few 
species of Asterina typical hyphopodia are not developed, their place being 
taken by so-called " node-cells," which are spherical or hemispherical, 
sw^ollen cells placed at regular intervals. These species may be regarded as 
intermediate forms betw^een the genus Asterina and genera like Asterinella 
(3), in which no hyphopodia are developed. 
The thyriothecium originates from a medial cell of a hypha, or from the 
terminal cell of a short lateral branch. In either case the initial cell divides 
rapidly and forms a group of small polyhedral cells between the hypha and 
the leaf surface. Each of the cells comprising this gioup begins to grow in 
a radial direction, each one forming a radiating hypha which is in close 
contact with its neighbour and is attached to it by the radial walls. The 
increase in circumference, as the disk increases in size, is provided for by the 
repeated bifurcation of the constituent hyphae. These are sometimes con- 
nected throughout their length, forming a compact disk with an entire or 
crenate margin; but more frequently they are free at the circumference, 
giving the thyriothecium a fimbriate appearance. The central part has 
meanwhile become arched to form the perithecial cavity, while the peripheral 
zone remains appressed to the leaf sui^face. Theissen regards this structure 
as a development of the complete spherical form found in the Perisjporiaceae ; 
the thyriothecium consists only of the basal half, which has been turned 
upside down, and hence is called "inverse." This inverse form, together 
with the radial-prosenchymatous structure of the membrane, is typical of the 
thyriothecia of the Microthyriaceae proper. 
The thyriothecium has no typical ostiole ; at maturity the initial group 
of cells may break away, forming a central pore, but the spores usually 
escape — in the genus Asterina — through radial or irregular fissures in the 
membrane. In Lemhosia and its allied genera the thyriothecium dehisces 
by a longitudinal slit, and in the genus Englerulaster the outer membrane 
