THE THALLUS 297 



His third group includes those forms that grow in crowded tufts or 

 swards such as CI. rangiferina, CI. furcata, CI. gracilis, etc. They originate, 

 as did the pyxidata group, in some Floerkeana-\\k& form, but in the "rangi- 

 ferina" group instead^of cup-formation there is extensive branching. In the 

 closely packed phalanx of branches water is retained as in similar growths 

 of mosses, and moist conditions necessary for fertilization are thus secured 

 as efficiently as by the water-holding scyphus. 



Sattler in his argument has passed over many important points. Above 

 all he ignores the fact that whatever may have been the original nature 

 and function of the podetium, it has now become a thalline structure and 

 provides for the vegetative life of the plant, and that it is in its thalline 

 condition that the many variations have been formed ; the scyphus is not, 

 as he contends, a new thallus, it is only an extension of thalline characters 

 already acquired. 



8. PiLOPHORUs, Stereocaulon and Argopsis. These closely related 

 genera are classified with Cladonia as they share with it the twofold thallus 

 and the lecideine apothecia. The origin of the podetium being different 

 they may be held to constitute a phylum apart, which has however taken 

 origin also from some Biatora form. 



The primary thallus is crustaceous or minutely squamulose and the 

 podetia of Pilophorus, which are short and unbranched (or very sparingly 

 branched), are beset with thalline granules. The podetia of Stereocaulon 

 and Argopsis are copiously branched and are more or less thickly covered 

 with minute variously divided leaflets. Cephalodia containing blue-green 

 algae occur on the podetia of these latter genera; in Pilophorus they are 

 intermixed with the primary thallus. 



The tissue systems are less advanced in these genera than in Cladonia : 

 there is no cortex present either in Pilophorus or in Argopsis or in some 

 species of Stereocaulon, though in others a gelatinous amorphous layer 

 covers the podetia and also the stalk leaflets. The stalks are filled with 

 loose hyphae in the centre. 



BB. Lecanorales. This second group of Cyclocarpineae is distinguished 

 by the marginate apothecium, a thalline layer providing a protecting amphi- 

 thecium. The lecanorine apothecium is of a more or less soft and waxy 

 consistency, and though the disc is sometimes almost black, neither hypo- 

 thecium nor parathecium is carbonaceous as in Lecidea. The affinity of 

 Lecanora is with sect. Biatora, and development must have been from a 

 biatorine form with a persistent thallus. The margin or amphithecium 

 varies in thickness : in some species it is but scanty and soon excluded by 

 the over-topping growth of the disc, so that a zone of gonidia underlying 

 the hypothecium is often the only evidence of gonidial intrusion left in 

 fully formed fruits. 



