BRITISH LICHENS. 27 



The lirelline* apothecium is that which forms an elevated ridge, 

 with an opening in the form of a sht running along the top. It prevails 

 in the pictorial Lichens, those which resemble writing, as OpegmplM and 

 Graphis. The receptacle here is usually black, and consists of a firm 

 cellular- substance, and is generally called the pcrithccium] . If the 

 perithecium entirely sun-ounds the thalamium, it is called entire (Fig. 20 ;) 

 if it be deficient beneath, it is called dimidiate. (Fig. 18.) The lireUse 

 are very variable in form, being immersed or slightly elevated, broad or 

 narrow, straight or curved, simple or branched. 



The pyrenodine\ apothecium is that in which the excipulum consists 

 of a closed receptacle composed of a dense leathery or brittle substance, 

 with a minute pore at the top caled the ostiolitm^. It may be globose or 

 conical, superficial, i.e., seated on the surface, or immersed in the thallus. 

 As in the lirelUue apothecium, if it surround the thalamium it is called 

 entire, and if deficient beneath it is called dimidiate, and also has the 

 name perithecium apphed to it. It is the characteristic form in 

 Verrucaria, approaching very closely the genus Sphceria in fungi. 



These various devices of nature presented to us in the structure of 

 the apothecium of Lichens are directed towards one object — the develop- 

 ment, protection, maturing, and dispersing those important bodies, the 

 spores. As we have before hinted, these bodies being regarded as the 

 female organs, we must now turn our attention to the organs designed 

 for their fertilisation. These are behoved to exist in the Spermaxjonia and 

 the Pycnides, which shall now be briefly described. 



The .^pei-magonia are mmute spherical bodies found on the surface 

 of or embedded in, the cortical layer of the thallus. If one of these be care- 

 fully dissected through the middle it will be found to have its interior 

 lined with excessively minute thi-ead-shaped jointed upright bodies, (Fig. 

 14e,) which are called sterigmata. From the summits, and also from the 

 joints of these arise still smaller, rod-like cyhndrical bodies, which are 

 either straight or curved, these are the spermatia. They are produced in 

 great numbers, and find their way through an opening in the summit of 

 the spermagonium into the open air to perform their function of fertilising 

 the hymenium of the apothecium. 



The pycnides are minute dark-coloured bodies somewhat spherical in 

 form, seated on the cortical layer of the thallus, the interior of which is 

 lined with a layer of simple upright filaments bearing on their summits 

 spore-hke bodies, which are called stylospores, (Fig. 15, a, b, c.) The fila- 

 ments bearing the stylospores are called basidia. The stylospores are 

 allowed to escape by a pore in the summit of the pycnides. We have now 

 completed the di'ier part of our subject, not without i-egretting that 

 so many hard names have had to be used to convey our meaning, the 



* From lirella Latin for furrow. 



+ From 'ire pi, around, and Ovi^Vf a sack. 



t From pyreyi, Latin for kernel, or stone of fruit. 



§ From ostiolum, Latin for a little door, 



