INTRODUCTION xvil 
continually formed. It is therefore no unusual experience to 
find the spores shed in seemingly well-fruited lichens. 
Lichen spores vary considerably in size, form, septation and 
colour. Usually there are 8 in the ascus, but in some genera or 
species the ascus contains only one large spore, in others they 
are innumerable and of small dimensions. The largest spores 
are found in Pertusaria and in Varicellaria, the 1-septate spore 
of the latter measuring up to 350 » x 115 p. In the family, 
Physiacez, the cross wall of the septate spore is so thickened 
that the lumen of each cell is reduced to a small area at the 
ends ; hence the term polari-bilocular. This is a type of spore 
without any parallel among fungi. Each 
cell of a septate spore may give rise to a 
hyphal filament on germination. The large 
one-celled spores of Pertusaria and other 
lichens contain many nuclei and produce 
germinating tubes all over the surface 
(fig. 11). The newly formed hyphal fila- 
ments become associated with an algal cell, 
and development proceeds (fig. 2), or, if no Pere Ch eee 
alga is encountered, the hyph in time die 9 ee Ne tine Cate 
off. In some genera of Pyrenocarpacer — (Ajter de Bary. x about 
(Endocarpon and Staurothele) gonidia occur 
in the hymenium alongside of the asci. They escape from the 
perithecia with the spores and together they build up a new plant. 
Spermogones or Pycnidia.—These are small perithecia-like bodies 
which occur on many lichens, generally scattered over the thallus, 
but occasionally confined to definite areas: to the periphery of 
the lobes (Parmelia physodes), the margins (Cetraria islandica) 
or the tips of the podetia (Cladonia). They vary in form, being 
ovoid, globose, etc., and sometimes irregular with folds of tissue 
projecting inwards, thus subdividing the interior. The inner 
wall is lined by simple or branched hyphe, the sterigmata or by 
a cellular tissue on which spermatia are borne. The spermatia 
are usually minute, and more or less cylindrical, and are provided 
with a cell-wall and contain a nucleus, etc. Many lichenologists 
have looked on these bodies as the male organs of the plant 
bearing non-motile spermatia. They are largely functionless, 
and as germination of the “spermatia” has been observed in a 
number of forms, it seems probable that they should rank as 
secondary fruit forms or pycnidia, their contents would then be 
more properly described as sporophores and pyenidiospores. 
