ously shaped but for the most part rounded, organic bodies, 

 which differ more or less in colour from the thallus over which 

 they are besprinkled, or to which they are attached, or in 

 which, more rarely, they continue normally immersed ; and gen- 

 erate the spores. The essential parts of the apothecium are 1, 

 the proper exciple, which contains all the other organs, but is 

 itself reduced, in a very large proportion of the Parmeliacei, to 

 a layer of cells (hypothecium) wholly concealed by the thalline 

 receptacle characteristical in this tribe ; and 2, the hymenium, 

 consisting of thekes (theca3; the spore bearing organs) inter- 

 mingled with slender, erect filaments (paraphyses), which latter 

 are sometimes undistinguishable or obsolete. The evolution of 

 the paraphyses and thekes will be noticed when we consider the 

 spermogones. 



Spores are cells capable of germinating, and are developed 

 in the thekes, which constitute, with the paraphyses, the hy- 

 menium. The spore-differences are numerous, and various; 

 and their systematic value, in plants offering so many difficul- 

 ties of arrangement as the Lichens, is unquestioned : but this 

 value was at first overestimated, and too much made of certain 

 particulars ; as, on the other hand, in the reaction against the 

 method of Massalongo, too little stress was sometimes laid on 

 certain others. Less weight, in this view, should be given to 

 spore-differences of a merely gradal character, or such as de- 

 pend only on dimensions, or number ; and more to such as seem 

 to have claims to be regarded as typical. Analysis appears to 

 indicate two well-defined kinds of lichen-spores, complemented 

 (may we say ?) in the highest tribe only, by a well-defined inter- 

 mediate one. In one of these (typically colourless) the origi- 

 nally simple spore, passing through a series of modifications, 

 always in one direction, and the spore tending constantly to 

 elongation (as e. g. in the genus Lecanora), affords at length the 

 needle-shaped (acicular) or now thread-shaped type. To this 

 is opposed (most frequently but not exclusively in the lower 

 tribes, and even possibly anticipated by the polar-bilocular sub- 



