FAMILIES AND GENERA 305 



The apothecia are partly formed from the thallus : Lecanora^ Parmelia, etc. The 

 Pyrenolichens are also included by him in this class, because "the thallus surrounds and 

 is concrete with the partly or wholly immersed apothecia." 



Class III. Homothalami with two orders, Scutellati and Peltati. The apothecia are 

 formed from the cortical and medullary tissue of the thallus : Ramalina, Usnea, Collema, 

 etc. 



Class IV. Athalami, with but one sterile genus, Lepraria. 



The orders are thus based on the form of the fruit; the genera in the 

 Synopsis number 41. Large genera such as Lecanora with 132 species are 

 divided into sections, many of which have in turn been estabhshed as 

 genera, by S. F. Gray in 1821, and later by other systematists. 



The Synopsis was the text-book adopted by succeeding botanists for 

 some 40 years with slight alterations in the arrangement of classes, genera, 

 etc. 



Wallroth' and Meyer^ followed with their studies on the lichen thallus, 

 and Wallroth's division into "Homoiomerous" and "Heteromerous" was 

 accepted as a useful guide" in the maze of forms, representing as it did 

 a great natural distinction. 



f. SCHAERER. This valiant lichenologist worked continuously during 

 the first half of the nineteenth century, but with very partial use of the 

 microscope. His last publication in 1850, an Enumeration of Swiss Lichens, 

 was the final declaration of the older school that relied on field characters. 

 His classification is as follows : 



Class I. Lichenes Discoidei, with ten orders from Usneacei to Graphidei ; fruits 

 open. 



Class II. Lichenes Capitati, with three orders': Calicioidei, Sphaerophorei and Cla- 

 doniacei ; fruits stalked. 



Class III. Lichenes Verrucarioidei, with three orders: Verrucarii, Pertusarii and 

 Endocarpei : fruits closed. 



An "Appendix" contains descriptions of Crustacei and Fruticulosi, all 

 sterile forms, except Coniocarpon and Arthonia, which seem out of place, 

 and finally a "Corollarium" of gelatinous lichens all classified under one 

 genus Collema. 



d. MassALONGO and Koerber. As a result of their microscopic 

 studies, these two workers proposed many changes based on fruit and 

 spore characters, and Koerber in the Sy sterna Licheniim Germaniae {i?)S^) 

 gave expression to these views in his classification. He also made use of 

 Wallroth's distinctions of "homoiomerous" and "heteromerous," thus dividing 

 lichens at the outset into those mostly with blue-green and those with bright- 

 green gonidia. 



1 Wallroth 1825. ^ Meyer 1825. 



S. L. ■ 20 



