REPRODUCTIVE ORGANS OF LICHENES. 389 
The apothecia may be either sessile or stalked ; the stalk, when 
present, is termed the podetium. ‘The apothecium is either com- 
posed of two parts, called the thalamiwm and excipulum, or, of 
the former only; when the latter is found, it forms a partial or 
entire covering to the thalamium. The body of the apothecium 
constitutes the thalamiwm, and the layer of cells at the bottom 
of this, upon which the thecze and paraphyses are placed, is 
termed the hypothecium. When the apothecium is divided by a 
vertical section, it is seen to contain a number of spore-cases called 
asct (fig. 853, as), surrounded by thread-like or somewhat club- 
shaped filaments, called paraphyses, par, which are usually re- 
garded as abortive asci; the asci and the paraphyses are placed 
perpendicularly upon the hypothecium. ‘The apothecia are fre- 
quently of a different colour from the surrounding thallus ; this 
is due either to the paraphyses or the excipulum. Each of the 
ascl, as, generally contains eight spores, but in some cases only 
four, and in others sixteen; thus the spores are commonly a 
multiple of two, and the number is always constant for each 
species. In rare cases the asci have a large number of spores, 
and are hence said to be polysporous. The spores themselves 
are usually termed ascospores. Some of these spores are of a very 
complex structure, being divided into two, four, or many cells. 
They are frequently coloured, and form beautiful objects under 
the microscope. 
In a very few genera of Lichens, as Abrothallus and Seutula, 
certain structures have been discovered by Tulasne, called stylo- 
spores. ‘They consist of isolated spores borne upon shortish 
simple stalks. They are produced in conceptacles to which is 
applied the name of pycnidia.’ 
The spermogonia were first discovered by Tulasne, but they 
have now been found in a great number of Lichens, and probably 
exist in all. They generally appear as little black specks near 
the margins of the thallus, in the tissue of which they are 
usually more or less imbedded (jig. 852, sp); but rarely, they 
are quite free and above the thallus. The spermogonium varies 
in form, and has one or more cavities, with a small orifice at the 
top termed the ostiole or pore (fig. 854, os), with which all the 
cavities communicate. The spermogonium, when mature, has 
its interior filled with a number of bodies called spermatia (figs. 
854, s, and 855, s), raised on stalks, termed sterzgmata or sper- 
matophores (figs. 854, sp, and 855, sp). The form of the sper- 
matophores varies much : according to Henfrey, ‘The simplest 
are short slender stalks, simple or branched; or they are 
articulated branches composed of a great number of cylindroid 
or globular cells (fig. 855, sp); or the branches are reduced to 
two or three elongated cells. The spermatia (fig. 855, s), are 
terminal on the spermatophores, and consist of exceedingly 
minute bodies, ordinarily linear, very thin, short or longish, 
straight or curved, without appendages, and motionless, and lie 
