292 POPULAR HISTORY OF LICHENS. 



Thallus consists of a number of contiguous, orbicular or 

 polygonal, minute, greenish scales. 



Leighton has arranged under this species several varieties 

 which belong doubtfully to the genus Undocarpon. The two 

 commonest varieties, which occur on alpine rocks in various 

 parts of Scotland and England, are classed by Schserer under 

 Lecanora cervina, one of the squamulose Lecanoras. This 

 seems to us a more appropriate position for these Lichens, 

 whose fructification however is decidedly anomalous. They 

 are distinguished by their spores being innumerable ; we have 

 hitherto found eight to be the average or maximum number 

 in each theca. The spores are very small, oblong or linear- 

 oblong, pale yellow, and exhibit a lively Brownian movement 

 in water, which Leighton describes as a "very peculiar, quick, 

 wriggling, spontaneous motion, as in a dance, setting and 

 retiring one from the other in quick succession He is in 

 error however when he compares this movement to that of 

 the zoospores of the Algse, and attributes its causation, theo- 

 retically, to the presence of cilia. (E. B. 1512, var. smarag- 

 dulum ; 2657, var. rufescens ; 215 2, var. privigna.) 



Var. Sinopicum is remarkable for its brick-red colour, 

 which is probably due to peroxide of iron taken up from 

 the soil. (E. B. 1776.) Under the lens may be discovered 



