474 



BOTANY 



PART II 



the fructification and the paraphyses originate from hyphae which arise below the 

 carpogonium. The fructification may arise from one or from several carpogonia. 

 The behaviour of the sexual nuclei requires further investigation. Such carpogonia 

 have been shown to give rise to the fructifications in a large number of genera. 

 In other genera (Peltigera, Solerina] they are reduced, the trichogyne is wanting, 

 and the reproduction is apogamous. Spermogonia are as a rule not found in these 

 cases, or are, as in the case of Nephromium, clearly degenerating structures. It 

 has been shown by A. MOLLER that the spermatia of Lichens can germinate and 

 produce a mycelium ; but this is not inconsistent with their primitively sexual 

 nature. 



The behaviour of Oollema pulposum is very remarkable. According to 

 F. BACHMANN the spermatia arise in the interior of the thallus in small groups 

 on the hyphae, and do not become detached. The elongated terminal cell of the 

 trichogyne remains in the thallus. but grows towards the spermatia and fuses 

 with them ( 9 a). 



A 



2. Basidioliehenes (Hymenolieehnes) ( 91 ) 



The Hymenolichenes are represented by Corapavonia, of which the genera Dictyo- 

 nema and Laudatea are only special growth forms. This Lichen is widely spread 



in the tropics, growing on the soil or on 

 trees. The fungus of this Lichen belongs 

 to the family Thelephoreae (p. 463) ; its 

 flat, lobed, and often imbricated fructi- 

 fications are also found entirely devoid 

 of Algae. In symbiosis with the uni- 

 cellular Alga Chroococcus it forms the 

 fructifications of Cora pavonia (Fig. 

 431), resembling those of the Thelephoras 

 with a channelled, basidial hymenium 

 on the under side. Associated sym- 

 biotically, on the other hand, with fila- 

 ments of the blue-green Alga Scytonema, 

 if the Fungus preponderates, it produces 

 the bracket-like Lichens of the Didyo- 

 nema form, found projecting from the 

 branches of trees with a semicircular 

 or nearly circular thallus, having the 

 hymenium on the under side. When 

 the shape of the thallus is determined by the Alga, a Lichen of the Laudatea 

 form occurs as felted patches of fine filaments on the bark of trees, with the 

 hymenium on the parts of the thallus which are turned away from the light. 



OFFICIAL. The only representative of the Lichens is Cetraria islandica 

 (LICHEN ISLANDICUS). Lobaria pulmonaria is also used in domestic medicine. 



The Manna Lichen (Lecanora esculenta) is a crustaceous Lichen that often 

 covers the ground to a depth of 15 cm. in the Steppes and Deserts of Southern 

 Russia, Asia Minor, and North Africa. The thallus falls into pieces the size of a 

 pea, and is thus readily swept by the wind ; it is used by the Tartars, who prepare 

 earth-bread from it. Cetraria islandica also, when the bitter substances are 

 removed by washing, may, owing to the abundant carbohydrate material (Lichen 

 starch) it contains, be used to make bread as well as to prepare jelly. Cladonia 



B 



FIG. 431. Cora pavonia. A, Viewed from above ; 

 B, from below ; hym, hymenium. (Nat. size.) 



