LINDSAY, ON ABROTHALLUS. 45 



confluent. In the latter case only two or three apotliecia 

 were usually in apposition ; tlieir margins, though modified 

 by pressure, were distinct, and their surface was flattened. 

 So flattened, semi-immersed, and inconspicuous have the 

 apotliecia of A. Smithii sometimes been in Highland 

 specimens, that I have mistaken them, by the naked eye, for 

 those of A. oxijsporus. I have also seen them, in the old 

 state, immediately prior to their fallmg out, when their base 

 of adhesion is constricted to a very narrow peduncle, capitate 

 or substipitate. The apotliecia of var. « are sometimes 

 exasperate or slightly black-pulverulent; or, still more 

 rarely, in Highland specimens, they have appeared to be 

 faintly marked by striae or gyras, like those of some of the 

 Urabilicarias. Another basis whereon Tulasne founds his 

 specific distinctions, is the presence or absence, as well as the 

 degree, of green-pulvarulence, of the apotliecia. According to 

 that observer, the apotliecia of A. Smithii are " sparsim 

 virenti-pulveruientis aut glabris;" those of .4. IFelwitzschii 

 are " pulvere chlorino velatis •/' while in regard to those of 

 A. microspermus, he remarks, "nee pulvere m virentem ei 

 inspersum vidi." The green-pulveridence, I believe, is 

 merely an illustration of the pulverulent or pruinose condition 

 of the apotliecia, so common among lichens, and which is one 

 form of sorediiferous degeneration. The green povrder, which 

 varies greatly in degree, consists chiefly of gonidia ; as do 

 also the globose, greenish, powdery wai'ts, resembling, in 

 general appearance, the apotliecia, in var. ii pulveruhntus, 

 which I have met with occasionally on the same thallus, — as 

 in specimens from Craig-y-Barns, Dunkeld. These warts 

 are generally less regular in form than the apotliecia in 

 question, from Avhicli, however, they are sometimes indis- 

 tinguishable without the microscope. I have repeatedly seen 

 black and green-pulverulent apotliecia occurring on the same 

 thallus : but in certain localities the former predominate ; in 

 others the latter. On Ben Lawers I found only black 

 apotliecia; on Craigie Hill, Perth, the green-pulverulent 

 ones are abundant. The latter 1 have noticed chiefly in 

 damp, shady places — precisely the situations favorable to 

 sorediiferous degeneration. 



The development of the tliecse and spores resembles what 

 obtains in the majority of other lichens. The theca arises 

 from the hypothecium as a small, colourless, spherical cell, 

 which gradually becomes elongated upwards so as to acquire 

 a clavate form. It contains at first a colourless, minutely 

 granulai' or amorphous protoplasm, which fills its whole 

 cavity. Gradually this is limited by the spore-sac^ which is 



