118 DR LAUDER LINDSAY ON THE SPERMOGONES AND PYCNIDES 
sterigmatic cell would appear to give off in succession many spermatia; hence the 
infinite numbers in which the latter are found in the spermogonal cavity. 
Emission or expulsion from the Spermogone.—When thrown off from the 
sterigmata, the spermatia accumulate in the central cavity of the spermogone, 
and gradually escape by the ostiole or pore. The emission or expulsion takes 
place under the influence of moisture, and its mechanism is the same in principle 
as that which regulates the expulsion of the spore from the thecee and apothecia. 
The nucleus or sterigmatic portion of the spermogone imbibes water with great 
rapidity and avidity, swelling much; while the capsule or envelope does so 
much less readily and more slowly. The result is, that under the influence of 
moisture, a considerable pressure is exerted by the latter upon the former, the 
spermogonal cavity is contracted in size, and its contents,—the spermatia and the 
mucilage in which they are imbedded,—are squeezed out of the ostiole with con- 
siderable force, frequently, indeed, as if in a cloud or stream. 
3. Cavity.—The spermogonal cavity is simple in the majority of lichens; but 
it is divided into a series of compartments or loculi, with more or less sinuous 
walls, in some Physcias, Coccocarpias, Usneas, Ramalinas, Thamnolias, Stereo- 
caulons, and Neuropogons. 
It contains a mucilage, which is usually colourless ; but which is rose-red in 
some Cladonias. In this are imbedded the spermatia. The cavity is sometimes 
occupied by a net-work of anastomosing filaments, which arise from among the 
spermatiferous sterigmata, and which appear themselves to be hypertrophied, 
sterile, modified sterigmata. In age, the sterigmata frequently encroach upon the 
spermogonal cavity so much, by becoming elongated and hypertrophied, that 
it is frequently at length obliterated. ; 
4. Ostiole or Pore—Form.—It is normally regular and round; but in the old 
state it is very frequently stellate-fissured, or otherwise irregular in its out- 
line. In wart-shaped spermogones it is also frequently elongated and irregular. 
In position, it is central, one being seated on the apex of each spermogone. But 
when the spermogones are confluent, the ostioles are frequently so also, or a mass 
of confluent spermogones may be dotted over with an irregular series of foramina 
or ostioles, as in the case of Alectoria Taylori, and Neuropogon melaxanthus. The 
ostiole may be either flat,—that is, even with the surface of the thallus,—papille- 
form, or depressed; or it may possess all three forms in the same species, or even 
specimen. But the papillaform ostiole is more common than either of the other 
two. It is frequently surrounded by, or seated in the centre of, a round areola, 
as in many Stereocaulons, Spherophorons, and Parmelias. | 
The lips or margins of the ostiole in the young and mature state are seldom 
very prominent; but in the old state they are frequently swollen, coloured, and 
prominent. 
Size.—The ostiole is generally very minute; invisible without the aid of the 
