FINK—THE LICHENS OF MINNESOTA. 27 
very limited (pl. 45, fig. 5, facing p. 217), or it may be extensive, as 
in most Arthonias. Careful statements as to the branching are made 
with the description of each species, but branching is so common 
and its character so difficult to trace that it may well be doubted 
whether the branching has any great diagnostic value. The par- 
aphyses are usually distinct, but sometimes the walls are more or 
less gelatinized and the whole structure in some+degree coherent 
and indistinct. They are usually longer than the asci, but are 
shorter than these in the case of the Verrucarias, in which they also 
become imperfectly or often wholly gelatinized. The tips, or apices, 
are usually thickened and darker in color than the remaining part. 
Other portions of the paraphysis may be somewhat colored; but 
usually the single organ appears quite hyaline, though the section 
of the hymenium often shows color. The functions are those of pro- 
tecting the asci and the contained spores against too rapid transpira- 
tion and of aiding in the dispersion of the spores. The thickening 
and coloration of the apices aid in the protective function. 
THE ASCI. 
The asci arise, like the paraphyses (pl. 18, fig. 8, a, facing p. 131), 
from the tissues of the hypothecium, or also from special ascogenous 
hyphe. They are usually shorter and wider than the paraphyses 
which surround them. In form they are most commonly clavate, 
but they may be cylindrical, pyriform, subglobose, or variously ven- 
tricose or otherwise irregular. The walls are usually more or less 
thickened toward the apex, probably by an accumulation of epi- 
plasm (pl. 18, fig.5,a,facing p. 131). The thickening may be very slight 
or it may occupy the upper third or more of the entire length of the 
ascus, as in some Arthonias. There is a succession of asci produced 
in each apothecium, and one may rarely find asci of two generations 
together, those of one generation containing mature or perhaps old 
and shriveled spores, and those of the other younger, larger, and un- 
shriveled ones, perhaps also immature, as shown by color or condition 
of cell division. In Calicium and other closely related genera the 
upper portion of the wall of the ascus becomes gelatinized and dis- 
solved before the spores are mature, and the spores escape and ripen 
in the hymenium outside the asci. In other ascomycetous lichens 
the spores mature within the asci, which then open at the apex for 
their eseape. The apical wall may rupture irregularly, the end may 
become torn across in some regular way, or probably in many in- 
stances an apical plug is pushed out, as in some other ascomycetous 
fungi. However, there is lack of any extended observations as to 
the method of opening of the ascus in lichens. 
