50 LICHENALES. [Thallogens. 



same size and colour. Threads from the two strata, proceeding in opposite directions, 

 penetrate each other. The apothecia consist of two principal parts, the one seated 

 above the other : the lower wall gives off threads which our author calls prosphyses, 

 the tips of which bear cylindrical cells, endowed with spontaneous motion, sometimes 

 growing singly, sometimes forming short chains, which are either terminal or lateral. 

 The upper surface, or hymenium, produces the female prosphyses directed downwards, 

 while an intermediate stratum, seated just above the point of production of the 

 androspores, consists of a quantity of female gonidia, from whence proceed the asci 

 and paraphyses. In the dioecious species the male apothecia are distinct, and the 

 individuals which produce them are described under the names of Pyrenothea, 

 Cliostomum, &c. 



After the far more careful and extended observations of Tulasne, there can be little 

 doubt that the principal part of these speculations is founded in error. 



The spermogones, M. Tulasne states, vary somewhat in structure, but they are all 

 formed essentially upon the plan above described. They are mostly plunged in the 

 substance of the Lichen, but are occasionally superficial like the shields of gymno- 

 carpous Lichens, as in Cetrarias, Cladonias, &c. In form they are generally globular, 

 elliptical, or irregularly oblong ; sometimes with a sinuous outline. The shell, 

 usually hard and crustaceous, varies much in thickness ; it is often black, or dark 

 coloured, especially towards the summit of the spermogone ; in other cases it is so 

 pale as to be lost among the surrounding tissue. Its cavity may be simple, undivided, 

 or multiple and divided in different ways into a variable number either of separate 

 pockets or of narrow sinuosities, all communicating with a common aperture. The 

 tissue which fills the spermogones is very greedy of water. 



The spermatia are in all cases terminal or acrogenous with respect to the part which 

 bears them. They are usually linear bodies of excessive tenuity, very short or 

 somewhat long, straight or curved, destitute of appendages, motionless, and united 

 to a mucilage the presence of which is concealed by its extreme transparency. 

 Iodine colours them brown ; liquid ammonia appears not to exercise any influence 

 over them. They would be truly analogous to the antherozoids of Callithamnium 

 and other Sea-weeds, if they were not born naked instead of developing in a spiral 

 cell. M. Tulasne sees no objection to their performing the same function. 



Remarks to the same effect have been made by M. Bornet upon the common 

 Ephebe pubescens, referred by one author to Algals, and by another to Lichens. 

 He finds spermogones in this plant, abundantly, in little spheroidal swellings of the 

 branches of the thallus ; and in fusiform swellings of the same nature immersed 

 apothecia ; the latter being confined to one individual, and the spermogones to 

 another, this author, adopting the hypothesis of sexuality among Lichens, regards 

 Ephebe pubescens as being dioecious. Ann. sc, ser. 3, xviii. 155. 



With regard to the shields, or apothecia, the substance of M. Tulasne's observations 

 may be stated succinctly as follows. The hymenial tissue which invests the disk of 

 the open shield of Parmelia and similar Lichens rests on a layer of very fine cells, 

 whose structure is usually less regular than that of the epidermal layer. This layer 

 proceeds from the filamentous matter of the medulla, or rests immediately upon it. 



The disk of the shield consists entirely of paraphyses and thecae mixed together, 



placed vertically on the tissue from which they rise, as in the hymenium of the- 

 caphorous Fungi. These two parts hold together with such tenacity, that they can 



hardly be dissociated without the aid of chemical re-agents. In Parmelia parietina 



tincture of iodine, employed by itself, colours deep blue the amorphous sub-hymenial 

 tissue, the membrane of the thecae, and the paraphyses, with the exception of the 

 terminal cells of tho latter, which preserve their natural yellow colour, almost without 

 alteration. The addition of sulphuric acid after iodine has no effect upon the yellow 

 part. These seem to be general facts, to which however there are some exceptions. 



The paraphyses are certainly jointed, not simple as Meisner supposes. They are 



not abortive thecao, but bodies formed of lines of cells, of which the upper are short 

 and coloured. In order to see this fact distinctly, it is indispensable that the com- 

 pact elements of the shield should be disaggregated by some acid. The thick-sided 

 condition of the thecae is part of their proper nature, and is not caused by the secretion 



of intercellular matter, as has been said. Acids also show that the thecaj are really 



bodies attached to a parent cell by a point at the base, but are otherwise free, however 

 much they may be glued to the adjoining parts. Without the assistance of acids, 



this is not to be seen. The theory of Schleiden that the thecae and paraphyses are 



the terminations of the branches of a filamentous underlying structure is inadmissible. 



-The spores contained in the spore-cases or thecae of Lichens are much like those 



of Fungi, except that the former are very seldom spiny or warted. It is in fact only 

 in Solorina saccata and Thelotrema exanthematicum that M. Tulasne has seen such 



