ORGANS OF KEPRODUCTION. 



383 



Botany. At present we hare only to examine their reproduc- 

 tive organs, and of these even Ave can only afford space for a 

 general sketch. 



1. LiCHENES OR LiCHEKS. — The reproductive organs of 

 this large group of plants, are hy no naeans so well under- 

 stood as those of the Acrogenous Cryptogams already de- 

 scribed. From the researches of M. Tulasne and others, it 

 would appear that the reproductive organs of Lichens are of 

 three kinds, namely, of 1. Apoihecia of yaxious forms, containing 

 a number of spore-cases, called asci or ihecce, and which are 

 supposed to represent the female organs; 2. Spermogonia, sper- 

 magoniay or spermatogonia, which have been regarded by some as 

 antheridia or male organs; and 3. Pycnidia, containing styluspores. 



The opothecia are of various forms, and have received differ- 

 ent names accordingly. The more usual forms are round {fig. 

 819, ap) and linear; in the latter case they are commonly termed 

 lirellce (fig. 818). They maybe either sessile or stalked; in the 

 latter case the stalk has received the name of podeiium. The 

 apothecium is either composed of two parts, called the thalamium 

 and e.rcipuluvi, or, of the former only. The latter when present 

 forms a partial or entire covering to the thalamium. The body 

 of the apothecium constitutes the thalamium, and the layer of 

 cells at the bottom of this upon which the thecae and paraphyses 

 are placed is termed the hypothecium. When the apothecium is 

 divided by a vertical section, it is seen to contain a number of 

 asci or thecce, surrounded by thread-hke or somewhat club- 

 shaped filaments, called paraphyses {fig. 820), which are usually 

 regarded as abortive asci; the asci and the paraphyses are placed 

 perpendicularly upon the hypothecium. The apothecia are fre- 

 quently of a diff"erent colour to the surrounding thallus ; this is 

 due to the paraphyses or excipulum. Each theca generally 

 contains eight spores, but in some cases only four, in others 

 sixteen ; thus the spores are generally a multiple of two, and 



Fig. 818. Fig. 819. 



Figs.^20. 821. 



Fig. 818. Thallus of Opegrapha aim showing lirellse Fig. 819. Portion of the 



thallus of Pamielia parietina, with young apothecia, ap, and spermagmiia, sp. 



After Henfrey Fig. 820. A thcca, t, of a Lichen, surrounded by paraphyses. 



The iheca contains four spores or sporidia,i> Fig. 621. Oue of the spores of 



the above divided iuto two cells. 



