42 DR. NYLAKDER ON GONIDIA AND THEIR DIFFERENT FORMS. 
The gonidia in the lower portion of the cortical stratum 
originate and are inclosed in the cellules of that stratum, and 
subsequently, as the development of the same stratum progresses, 
the gonidia are observed in a free condition. In the “ Flora,” 
1874, p. 60, when touching upon points relating to tlie nutrition 
of Lichens, I have recorded in what manner the thalline develop- 
ment advances from the external to the internal parts, so that the 
external portions are the younger, and on the contrary the interior 
or medullary parts are of more advanced age, and at length often 
pass into a thickened mass (crassamentum), thence called “ tar- 
tareous ” thalli — a circumstance which renders Lichens, in a 
certain way, comparable with Coralline Polypi, or Madrepores, 
compelling the active life in the thin cortical- gonidial stratum and 
the nearest portions of the medulla, the interior or lower parts 
being almost inanimate or deposed, and not rarely exhibiting the 
worn particles of the medullary stratum (filaments and chiefly 
broken crystals).* 
The origin of chlorophyll (more correctly to be called, as I have 
formerly recommended, “ phyllochlore,”) takes place here not 
otherwise than in the cellules, e.g., of Mosses or Hepatica?. The 
primary difference to the eye consists in the circumstance that the 
gonidia often occur as discrete cellules, though, also (as will 
afterwards be seen), very many forms variously compounded are by 
no means wanting. True growing gonidia, either in a young or 
adult state, may be observed in the cortical cellules of Lichens best 
adapted for examination in this respect. I have mentioned Um- 
bilicaria, m the ‘‘Flora,” 1875, p. 303; while equally distinctly 
Physcia lithotea,\ endococcina, pulverulenta, Psoroma hypnorum, 
&c., commend themselves to the same observation, and at the same 
time others, situated lower and free amongst the myelohyphee, to 
which by reason of the gelatine penetrating all the elements the 
gonidia adhere, though they are by no means truly adnate, as 
writers who readily believe what they wish have affirmed. The 
cortical stratum gradually growing or unfolding itself, but during 
the same time being in like proportion dissolved beneath (or 
resorhed, as it is called in physiology), the gonidia become free. 
Thus whether inclosed in the cellules or conjoined together or 
discrete, these always constitute the organic system, and indeed the 
physiological centre, of the thallus. And since the biological 
* This is best shown in the thicker crnstaceons thalli. But chondroicl axes 
(solid or hollow), e.g., of TJsneoe and Cladonioe, present only another method 
of an analogous circumstance : for when I’ightly considered these axes 
answer to the lower surface of the thallus descending into itself ; they 
play a part opposed to the upper (superficial) cortical stratum, and form 
in their own way an internal cortical stratum. 
t This species is to be separated fi'om Fh. ohscura, inasmuch as it has a 
different thalline texture. Of Fh. lithotea, sciastra (Ach.), is a variety; and 
there is also another corticole vaxiety, sciastrella, Nyl., collected near Eich- 
staett by Arnold. Fhyscia endoccocina is allied to lithotea and not to Fh. 
ohscura. 
