288 PHYLOGENY 



lichen fructification. It has been stated that the greatest advance of all 

 took place with the formation of a cortex over the primitive granule, 

 followed by a restricted area of growth outward or upward which resulted 

 finally in the foliose and fruticose thalli. Guidance in following the course 

 of evolution is afforded by the character of the fructification, which generally 

 shows some great similarity of type throughout the different phyla, and 

 remains fairly constant during the many changes of thalline evolution. 

 Development starting from one or many origins advances point by point in 

 a series of parallel lines. 



a. Thallusof Pyrenocarpineae. Inthisseries there are two families 

 of algae that function as gonidia: Protococcaceae, consisting of single cells, 

 and Trentepohliaceae, filamentous. Phyllactidium (^Cephaleuros) appears in 

 a single genus, Strigula, a tropical epiphytic lichen. 



Associated with these types of algae are a large number of genera and 

 species of an elementary character, without any differentiation of tissue. In 

 many instances the thallus is partly or wholly embedded in the substratum. 



Squamulose or foliose forms make their appearance in Dermatocarpaceae: 

 in Normandina the delicate shell-like squamules are non-corticate, but in 

 other genera, Endocarpon, Placidiopsis, etc., the squamules are corticate and 

 of firmer texture, while in Dermatocarpon, foliose fronds of considerable size 

 are formed. The perithecial fruits are embedded in the upper surface. 



In only one extremely rare lichen, Pyrenothamnia Spraguei{^. America), 

 is there fruticose development: the thallus, round and stalk-like at the base, 

 branches above into broader more leaf-like expansions. 



b. Thallus of Coniocarpineae. At the base of this series are genera 

 and species that are extremely elementary as regards thalline formation, 

 with others that are saprophytic and parasitic. The simplest type of thallus 

 occurs in Caliciaceae, a spreading mycelium with associated algae (Proto- 

 coccaceae) collected in small scattered granules, resembling somewhat a col- 

 lection of loose soredia. The species grow mostly on old wood, trunks of trees, 

 etc. In Caliciumi^Chaenothecd) chrysocephaltim as described by Neubner' the 

 first thallus formation begins with these scattered minute granules; gradually 

 they increase in size and number till a thick granular coating of the sub- 

 stratum arises, but no cortex is formed and there is no differentiation of tissue. 



The genus Cypkelium (Cypheliaceae) is considered by Reinke to be more 

 highly developed, inasmuch as the thalline granules, though non-corticate, 

 are more extended horizontally, and, in vertical section, show a distinct 

 differentiation into gonidial zone and medulla. The sessile fruit also takes 

 origin from the thallus, and is surrounded by a thalline amphithecium, or 

 rather it remains embedded in the thalline granule. A closely allied tropical 



' Neubner 1893. 



