232 POPULAR HISTORY OF LICHENS. 



in appearance. The young thallus often contains such an 

 amount of oxalate of lime as to be quite gritty between glass 

 slides ; and under the microscope this salt may be detected 

 in the form of its characteristic octahedral crystals. Its 

 thecse are long, slender, and linear; its spores comparatively 

 large and very distinct. The latter are broadly oval or some- 

 what oblong, frequently with an irregular wavy or bulging 

 margin, depending upon their cellular contents, which con- 

 sist of a number of rounded cubical cellules, varying in size, 

 arranged usually in six to ten horizontal rows, and sometimes 

 in a distinctly double longitudinal series ; they are thus of 

 the class of spores termed cellular or muriform. When 

 young they are pale-yellow, but when mature they become 

 dark-olive or blackish or brownish-green. The spermogones 

 are scattered over the thallus, and sometimes niched in the 

 exciple of the apothecia ; they are difficult of discovery, from 

 the pale colour of the ostiole. They are oval or globular ; 

 their usually simple cavity is lined with straight sterigmata, 

 and almost loaded with spermatia, which are linear, straight, 

 and thicker than those of most Lichens. 



3. Urceolahia calcarea (calx, lime). Thallus tarta- 

 reous-farinose, whitish rimulose-areolate, often effigurate at 

 circumference; hypothallus white. Apothecia immersed, 



