FUNGI. 



469 



(formerly called gonidia) imbedded in the thallus (such as 

 Palmella, Nostoc, &c.), and forming regular organs of fructifica- 

 tion (apothecia) containing asci, in some cases known to be the re- 

 sult of a sexual process. There are 

 formed also on the thallus spermo- 

 gonia containing spermatia (the male 

 organs, which have been proved in cer- 

 tain cases to fertilize a female organ 

 called a trichogyne) and occasionally 

 pycnidia. - Illustrative Genera : 

 Opegrapha, Pers. ; Umbilicaria, 

 Hoffm. ; Verrucaria, Pers. ; Endo- 

 carpon, Hedw. ; Sphcerophoron, Pers. ; 

 Gladonia, Hoffm. ; Lecidia, Ach. ; 

 Stereocaulon, Schreb. ; Parmelia, Fr. ; 

 Stieta, Schreb. ; Getraria, Ach. ; 

 Roccella, DC. ; Ramalina, Ach. ; 

 Collema, Ach. 



Structure and Life-history. The para- 

 sitism of the fungal portion of the Lichen 

 thallus is not of such a nature as to 

 cause the death of the host alga, but the 

 relations seem to be so equally balanced 

 as to allow of the protracted mutual 

 existence of both. To illustrate this 

 and the life-history of the Lichenes 

 two instances will perhaps be sufficient, Fig.^516. 

 both of which are from the recent re- 

 searches of Dr. Stahl. 



Sexuality is not known to exist gene- 

 rally in the Lichenes ; but since it has 

 been established in the Collemacece (an 

 important subdivision) we may fairly 

 conclude that the matter only wants 

 investigation to bring more instances 

 to light. In this subdivision the minute male cells or spermatia 

 are formed within closed receptacles called spermogonia, and, unendowed 

 with the power of motion, reach the female organs by the conduction of 

 water (rain, &c.). The female organs or trichogynes may be said to be 

 composed of three parts according to their function : (1) a unicellular organ 

 of conception, (2) a conductive canal, (3) an ascogonium in the form 

 of coils, also composed of several cells which, when fertilized, give rise 

 to the spores. The point of the trichogyne is protruded through the 

 surface of the thallus, in which the rest of the organ is imbedded, and 

 the spermatia coming in contact with it, the contents become amalgamated 

 witb the result of fertilization. The first result of the fertilization is seen 

 in the increasing size of the cells of the ascogonium, and also an increase 

 in their number by the formation of transverse septa. The paraphyses 



A. Fertile branch of the 

 thallus of Sphcerophoron coralloides, 

 with a, a perithecium, and 8, sper- 

 mogonia B. Thcae and para- 

 physes from the perithecium. C. 

 Spermatia from the spermo- 

 gonium. 



Fig. 517. A. Branch of Ramalina 

 fraxinea. B. A fragment with 

 apothecia. C. A section of a 

 fragment magnified, showing, a, 

 apothscium, and , spermogonia. 



