314 DR. D. D. CUNNINGHAM ON MYCOIDEA PARASITICA, 
interwoven film of empty filaments (corresponding with the cortical layer of other 
lichens) which covers the disks and the intervals between them (Pl. XLIII. fig. 19). 
Whilst this film is forming, changes occur in the disk beneath. The cells multiply 
greatly by the formation of tangential septa dividing the rays into rows of short spaces; 
and their contents pass from orange into bright green. Each of the cells now buds out ` 
below, and forms a rounded prominence on the inferior surface of the disk; and these 
buds, gradually absorbing all the contents of their parent cells, are ultimately detached 
as independent bright green circular cells, and form accumulations beneath the now 
empty framework of the disks (Pl. XLIII. fig. 16). The process begins from the centre 
of the disks, and gradually extends peripherally until the disks are left as empty cellular 
shields covering a mass of detached circular cells. The hyphæ of the cortical layer, 
after ramifying over the upper surface of the disks, finally force their way downwards 
between the constituent cells of the latter towards the central point from which the 
rays diverge. At the point of entrance a dense cellular mass of fungal cells is developed, 
eausing an appearance, very frequently to be observed in the disks of the mature lichen, 
of a central colourless space in the groups of gonidial cells (Pl. XLIII.fig.14). Having 
gained an entrance, the hyphs then ramify among the projecting buds on the under 
surface of the disk, and, becoming adherent to them, retain them in position when freed ` 
from their parent cells. The green gonidial cells continue to multiply by the division 
of their contents, and frequently form several strata, beneath which a colourless layer of 
hyphee is more or less distinctly developed. Owing to the ease with which the lichenous 
patches are detached from their position on the surface of the leaf, it is a matter of some 
difficulty to obtain good demonstrations of their structure; but the accompanying 
illustrations show the appearances present in successful vertical sections, as well as in 
cases in which masses of gonidia and hyphæ have been teased out from beneath their 
investing disks (Pl. XLIII. figs. 11, 17). | I 
At various points of the patch the filaments, sometimes those of the film, and more 
rarely those apparently of the intergonidial hyphæ, give origin to an inferior layer of 
loose tissue. This rapidly multiplies and forms dense whorls of tangled filaments, from 
which the spermogonia and apothecia are gradually developed; and it is only around 
these structures that any loose tissue corresponding to a medullary layer can be 
encountered (Pl. XLIII. fig. 20). | 
The spermogonia, as previously mentioned, are developed anteriorly to the apothecia. 
They ultimately appear as slightly elevated circular spots of a greenish-brown hue, 
measuring 0°175 millim. in diameter, and discharge their contents on the surface of the 
patch through minute rounded ostiola. The spermatia are colourless, slightly curved, 
and measure 0:004 by 0:001 millim. (Pl. XLIII. fig. 13). The apothecia measure about 
0-7 millim. in diameter by 0:2 millim. in height, and appear to the naked eye as 
minute blackish cups on the surface of the patch. They are invested by a distinct rim, 
derived from the cortical layer, and show the usual features presented by the apothecia of 
gymnocarpous lichens—being anatomically separable into excipulum, subhymenial layer, - 
hymenium, and nucleus, consisting of the remains of the whorls from which they are 
developed (Pl. XLIII. fig. 15). The asci contain eight curved uniseptate spores, and are 
