98 
THE FORMATION OF SPORES IN LICHENS AND FUNGI. 
spherical, especially dense and refractive in its upper part, as the 
examination of preparations preserved in alcohol demonstrates, 
d’he ascus augments in volume, the primitive nucleus disappears, 
and eight spores simultaneously arise in the superior part of the 
ascus. These spores approach eacli other closely, and absorb for 
their formation nearly all the superior protoplasm of the ascus. 
The spores appear complete. In the centre of each of them we 
observe a denser, although badly circumscribed spot. The young 
spores are at first solid, and surround themselves very rapidly with 
a colourless membrane of cellulose, which quickly increases in 
thickness. At the same time they increase in size, and their pro- 
toplasmic contents retire towards their walls. The denser, and at 
first central portion, which is an irregular or stellate granule, 
becomes equally parietal, and appears to be equivalent to a nucleus, 
for it immediately doubles {dedouble) itself, and displays between 
its two moieties a partition of protoplasm, by means of which the 
spore, which has become ellipsoid, is divided along its smaller axis, 
into two equal parts. But this nucleus is so small that we are 
unable to observe the details of its division. In the partition of 
protoplasm, there is formed at the same time, a new^ wall of cellu- 
lose, which speedily acquires a great thickness. The two small 
nuclei which generally are at first fixed near the new wall, cannot 
be distinguished from the other granular contents of the spores, 
until these acquire a greater age. 
Finally, the membranes of the spores which have become bicel- 
lular, rapidly acquire a colour, which becomes deeper and deeper, 
from grey to brown. The small quantity of protoplasm which 
surrounds the spores becomes tinted always, by iodine, of a yellow- 
brown. 
The development of the spores of Physcia ciliaris is conformable 
to that which may be observed in the asci of the Caliciei and 
Splicerophorei. Since in these instances the spores do not issue 
from the ascus, but the ascus divides itself into portions corres- 
ponding to the spores, these nevertheless do not arise from a 
division of the contents of the ascus, but rather from a free for- 
mation. These spores are arranged in a single longitudinal line, 
and from their first evolution employ nearly the whole of the con- 
tents of the mother cell ; afterwards, as they increase in size, they 
arrange themselves one above another against the wall of the 
ascus, and often give to this wall an embossed or swollen ap- 
pearance. 
Nevertheless, we are able, now and then, by compression, to 
make the spores, when mature, issue from the ascus, and if the 
membrane of the ascus is not speedily visible, it is altogether 
owing to its extreme delicacy, and the refraction of light by the 
spores. With regard to the division into two of the spores of 
Calicium trachelinum^ it is effected precisely as in Physcia ciliaris. 
W. 
