_a._ ORIGIN AND FORM OF SPERMATIA. Lichen spermatia arise at the tips of the sterigmata either through simple abstriction or by budding. In the former case—as in the _Squamaria_ type—a delicate cross-wall is formed by which the spermatium is separated off. When they arise by budding, there is first a small clavate sac-like swelling of the end of the short process or sterigma which gradually grows out into a spermatium on a very narrow base. This latter formation occurs in the _Sticta_, _Physcia_ and _Endocarpon_ types.
Nylander[726] has distinguished the following forms of spermatia:
1. Ob-clavate, the broad end attached to the sterigma as in _Usneae_, _Cetraria glauca_ and _C. juniperina_.
2. Acicular and minute but slightly swollen at each end, somewhat dumb-bell like, in _Cetraria nivalis_, _C. cucullata_, _Alectoria_, _Evernia_ and some _Parmeliae_, frequently borne on “arthrosterigmata.”
3. Acicular, cylindrical and straight, the most common form; these occur in most of the _Lecanorae_, _Cladoniae_, _Lecideae_, Graphideae, Pyrenocarpeae and occasionally they are budded off from arthrosterigmata.
4. Acicular, cylindrical, bent; sometimes these are very long, measuring up to 40 µ; they are found in various _Lecideae_, _Lecanorae_, Graphideae, Pyrenocarpeae, and also in _Roccella_, _Pilophorus_ and species of _Stereocaulon_.
5. Ellipsoid or oblong and generally very minute; they are borne on simple sterigmata and are characteristic of the genera _Calicium_, _Chaenotheca_, _Lichina_, _Ephebe_, of the small genus _Glypholecia_ and of a few species of _Lecanora_ and _Lecidea_.
In many instances there is more or less variation of form and of size in the species or even in the individual. There are no spherical spermatia.
_b._ SIZE AND STRUCTURE. The shortest spermatia in any of our British lichens are those of _Lichina pygmaea_ which are about 1·4 µ in length and the longest are those of _Lecanora crassa_ which measure up to 39 µ. In width they vary from about 0·5 µ to 2 µ. The mature spermogonium is filled with spermatia and, generally, with a mass of mucilage that swells with moisture and secures their expulsion.
The spermatia of lichens are colourless and are provided with a cell-wall and a nucleus. The presence of a nucleus was demonstrated by Möller[727] in the spermatia of _Calicium parietinum_, _Opegrapha atra_, _Collema microphyllum_, _C. pulposum_ and _C. Hildenbrandii_, and by Istvanffi[728] in those of _Buellia punctiformis_ (_B. myriocarpa_), _Opegrapha subsiderella_, _Collema Hildenbrandii_, _Calicium trachelinum_, _Pertusaria communis_ and _Arthonia communis_ (_A. astroidea_). Istvanffi made use of fresh material, fixing the spermatia with osmic acid, and in all of these very minute bodies he demonstrated the presence of a nucleus which stained readily with haematoxylin and which he has figured in the spermatia of _Buellia punctiformis_ as an extremely small dot-like structure in the centre of the cell. On germination, as in the cell-multiplication of other plants, the nucleus leads the way. Germination is preceded by nuclear division, and each new hyphal cell of the growing mycelium receives a nucleus.