LINDSAY, ON ABROTHALLUS. 61 



had abundant opportunities of observing the peculiar, 

 wriggling, swimming, and di\dng motion wliicli has at- 

 tracted the attention of so many lichenologists, and given 

 origin to so many ingenious theories as to its nature. But 

 I see no reason to doul)t for a moment that it is merely the 

 molecular or Brownian motion now so familiar to botanists. 

 The movements occur only in free, isolated, floating sper- 

 matia; en masse tliey are at perfect rest. Iodine had no 

 effect on the spermatia or sterigmata further than communi- 

 cating its own tinge ; but the network of tubes from which 

 the latter spring, or the intercellular matter, aj)peared some- 

 times to assume a bluish colour. 



It may be advisable here to point out the resemblances and 

 differences between the spermogones of the Abrothallus and 

 those of P. saxatilis. I have examined the spermogones of 

 P. saxatilis on various fiirfm-aceous forms from Norway, 

 Ben Lomond, the Kyles of Bute, and other localities. In 

 external characters they closely resemble those of the 

 Abrothallus. They occirr as extremely minute, black points 

 scattered over the surface and towards the extremities of 

 smooth lacinise. Each spot is perforated by an almost im- 

 percept-ble ostiole — simple or stellate — which leads into the 

 spermogonal cavity. The sterigmata which line its walls, 

 however, are very different from those of the Abrothalkis. 

 Here they are equally delicate and narrow ; but they are 

 articulated, ramose, and much longer. There is, however, a 

 great want of uniformity in length, some of them projecting 

 far beyond the others. The articulations consist of simple, 

 cylindrical cells, generally joined to each other at more or 

 less irregular angles. Spermatia are given off perpendicu- 

 larly, or at various angles from the apex of each articulation ; 

 consequently the sterigmata generate spermatia both from 

 their apices and sides. The latter, indeed, appear to come 

 off from the former as a series of minute lateral branches 

 or buds. The spermatia are very abmidant ; they are about 

 the same length as those of the Abrothallus, but they fre- 

 quently appear more slender. Korber describes " Spermo- 

 gonien auf den Runzeln des Lagers als schwarze gehaufte 

 Wiirzchen bisweilen wahrnehmbar, mit sehr kleinen, fast 

 kugligen [?] Spermatien " (p. 73) . In addition to the sterig- 

 mata there arises from the walls of the spermogone a series 

 of very delicate ramose filaments, which project far beyond 

 them, and fill its caAdty with a delicate network formed by 

 their anastomoses and ramifications. These filaments are 

 sterile. Sometimes they are articulated or septate at the 

 extremities, which may appear proliferous ; but this is pro- 



