LICHENS. 



[ 391 ] 



LICHENS. 



the spores in the following way : If a thin 

 vertical section is cut from the middle of the 

 apothecium, and divided so as to separate 

 the hymenium or hypothecium (or layer sup- 

 porting the thecae) from the subjacent tis- 

 sues, and the parts thus dissected are placed in 

 water, the hymenium becomes greatly curved, 

 presenting its external surface outwards and 

 convex, while the other part, representing 

 the body or excipulum of the apothecium, is 

 curved with equal force, but its upper extre- 

 mities are directed inwards to meet one 

 another. Thus it seems that both the 

 hymenial layer and the outer wall of the 

 apothecium eagerly absorb water, much 

 more than the tissues separating them. 

 Consequently when an entire apothecium is 

 wetted, the borders tend to approach one 

 another, curving inwards, while the layer 

 bearing the thecae becomes bulged out above, 

 whence arises a pressure on the thecae, ulti- 

 mately bursting them at the summit, and 

 causing the expulsion of their contents. 

 The expulsion of the spores of the Lichens 

 takes place slowly, while that of some Asco- 

 mycetous Fungi is sudden, which may be 

 accounted for by the different consistence of 

 the surrounding structures. 



Eight is generally set down as the normal 

 number of spores in each theca, but this is 

 not universal here any more than in the As- 

 comycetous Fungi; some species of Endo- 

 carpon, Parmelia, &c., have polysporous 

 thecae containing a considerable number, 

 while there are often less than eight. 



Stylospores. This name is given to cer- 

 tain very rare organs discovered by Tulasne 

 in Abrothallus and Scutula, consisting of 

 isolated spores borne upon shortish, simple 

 stalks. They are produced in conceptacles, 

 to which is applied the name of pycnidia. 

 They are closely analogous to the structures 

 of the same name found in some Fungi (see 

 STYLOSPORES). 



Mr, Berkeley has described another struc- 

 ture in Lecidea sabuletorum, namely a kind 

 of basidium, or enlarged cell supporting 

 spores, developed from some of the para- 

 physes. Tulasne questions the correctness 

 of the observation. 



Spermagonia. In addition to the preceding, 

 the Lichens exhibit another form of repro- 

 ductive organs, which are liable to be con- 

 founded with SphterifB and other Fungi 

 growing on the Lichens, or with parasitical 

 Lichens in similar positions. They appear 

 as black or brown points, usually near the 

 margins of the thallus (PI. 29. fig. 1), and 



have been found in Borrera, Parmelia, 

 Sticta, Cladonia, Collema, Opegrapha, Sphee- 

 rophoron, Lichina, Endocarpon, &c., and 

 seem to be universal. 



The spermagonia are closed receptacles, 

 resembling more or less the conceptacles of 

 the Hypoxyla among the Ascomycetous 

 Fungi. In most cases they are immersed in 

 the substance of the thallus (PI. 29. figs. 2 

 & 13), and are perceptible externally only 

 by a little projection, if at all ; in rare cases 

 they are free and borne above the thallus 

 (some Cladonice, Cetrariee, Gyalectce, &c.). 

 The ordinary form is globular, ellipsoidal or 

 irregularly oblong, and sometimes with a 

 sinuous outline. The spermagonia have 

 either a simple undivided cavity (PI. 29. figs. 

 13, 16), or multiple and divided in different 

 ways into a variable number either of sepa- 

 rate chambers or narrow cavities, all commu- 

 nicating with a common orifice, which is 

 the ostiole or pore of the apparatus. This 

 structure bears a close relation to that usual 

 in the Ascomycetous Fungi (Coniomycetous 

 forms, Cytispora, Septoria, &c.), and bears 

 testimony to the close relation between the 

 Lichens and Fungi. The form and dimen- 

 sions of the spermatophores, or peduncles of 

 the spermatia, vary much. . The simplest 

 are short, slender stalks, simple or branched, 

 or they are articulated branches composed 

 of a great number of cylindroid or globular 

 cells (PL 29. figs. 3 & 14) ; or the branches 

 are reduced to two or three elongated cells. 

 The spermatia are terminal on the spermato- 

 phores, and consist of exceedingly minute 

 bodies, ordinarily linear, very thin, short or 

 longish, straight or curved (PI. 29. figs. 3, 

 10, 15, 16), without appendages and motion- 

 less, and lie in a mucilage of extreme trans- 

 parency. The spermatophores and their 

 spermatia usually fill up the cavity of the 

 spermagonia, when just mature ; afterwards, 

 when the development is complete and the 

 spermatia discharged, the spermagODia are 

 found empty and discoloured. 



The minute bodies, called spermatia, are 

 regarded by most of those who have observed 

 them as analogues of the spermatozoids pro- 

 duced in the antheridia of the higher Cry- 

 ptogams. Itzigsohn imagined that he saw a 

 spontaneous motion of them when lying in 

 water beneath the microscope, but this ap- 

 pears to have been an error, and the only 

 movement really existing has been regarded, 

 probably most correctly, as merely molecular, 

 that universal in extremely minute bodies, 

 living or dead, lying in a fluid. 



