946 XII. LICHENES. 



■ Section IV. Phtllode^. 



Nephroma. Peltigeva. Solorina. Sticta. 



Parmelia. Physcia. Umbilicaria. 



Section V. PLACODEiE. 



Squamaria. Placodiiim. Lecanora. Urceolaria. Pertusaria. 



Thelotrema. Lecidea. Opegrapha. Chiodecton. 



Section VI. Pteenode^. 

 Bndooarpon. Verrucaria. Endococcns. Trypethelium, Sec. 



Several botanists are, however, now inclined to unite with Lichens the entire group of Thecasporeee, 

 Fungi which differ from them in no important character but the ahsence of a gonidial layer. The absence 

 of oxalate of lime in the tissue of Fungi, on which the separation of the two groups was founded, cannot 

 be relied on, since long ago Dawson Turner, Tripier and Steinheil proved chemically the presence of this 

 salt in certain Boleti {Boletus mlphurem, &c.). The action of iodine, which tinges with blue the sporangia 

 of most Lichens, does not appear to us sufficientto sepai-ate the Lichens and thecasporal Fungi. Our opinion 

 is corroborated by that of a learned botanist, Dr. L^veilliS, an authority on all questions relative to this 

 branch of cryptogamy, who has sent us a letter from which we extract the following passages : — 



'You enquire, my dear Decaisne, what is the difference between the Liichens and the thecasporal 

 Fungi : the question is definite, and cannot be evaded. I answer that I have frequently examined into 

 it, and I find the distinctions to be so trifling that I have always regretted that these vegetables should 

 not be placed under one head. The paraphyses, the thecfe and the spares are identical. The hypotlmllus ■ 

 of Lichens corresponds to the mycelium of Fungi ; like it it spreads over the surface of bodies, develops 

 under the epidermis of plants, in the thickness of tissues, and in the earth. The receptacle {apotheckmi) 

 of Lichens varies as much in form as that of Fungi ; it is sometimes superficial, sometimes sunk in the 

 tissues ; but in Lichens it is always, like the thallus, coriaceous. In Fungi it is often similar, and in 

 Pezisa it is fleshy, watery, or friable like wax. The surface of the receptacle (epithecium) is naked in 

 Fungi ; the extremity of the paraphyses, which often projects and colours the disk, is fugitive, and dis- 

 appears in the Fungus. In Lichens, on the contrary, the epithecium is a normal state ; it is formed, not 

 only by the swollen projecting extremity of the paraphyses, but by a granular and persistent matter. 

 Again, the receptacle of Fungi is fugacious ; but in Sphairiete, which continue for a long time, without 

 being perennial, the conceptacles only last a year at the most. SpJieeriece, once developed and fructified, 

 have completed their existence ; they do not vegetate afresh. "With Lichens it is different ; their 

 receptacle is perennial ; it may remain for several years, and always be in a perfect state of fructification. 

 This perennial condition of the receptacle has been noticed by Meyen, and I have verified it in Parmelia 

 parietina, and in P. Lagascai in Corsica. Also I have seen at Montmorency Lecanora snlphurea, of which 

 the disk (theciam) had been destroyed by snails, reproduce a new thecium. This phenomenon of the 

 reproductive organs, added to the character of the thallus of Lichens, and the (at most) annual existence 

 of the most compound Sphesrieai, I consider as one of the most curious and important of biological cha- 

 racters. Unfortunately it is I who have brought it forward and established it : it does not pass current 

 on the Exchange of Science. How can we distinguish a Lichen from an ascosporous Fungus, since the 

 reproductive organs are similar ? The only difference we can detect is in the thallus ; but if it is crus- 

 taceous, scaly, filamentose, &c., in Lichens and Sphcerieee, let us not forget that the thallus is the cha- 

 racteristic mark of Lichens, the more so as it is confined to them alone. The principal point then is to 

 establish the difference between the thallus of Lichens and the stroma of Fungi. That the one resembles 

 branches, the other a simple cushion, is a matter of indifference. The thallus of Lichens always presents 

 three layers : the cortical, the gonidial, and the medullary. The Splimriem, on the contrary, have but two • 

 the gonidial layer is always wanting: this is an anatomical truth which must perforce be admitted. 

 These gonidia,' by their presence, remove every difficulty when in doubt as to the nature of a Fungus or 



' Sachs has adopted in his ' Lehrbuch ' the views enter- as it were in captivity by the meshes of an ascomycetous 

 tained by Schwendener and ReesB, that Lichens are Fungus. This is an extension, in fact, to all Lichens of 

 not autonomous organisms, but colonies of Algse held a suggestion of De Bary's that Collema, Ephebe, &c., are 



