Trentepohliaceas 



309 



possible in some cases to discriminate between micro- and macrozoogonidia. 

 When the zoogonidium of Cephaleuros has 

 come to rest its protoplast frequently un- 

 dergoes a rejuvenescence and is then set 

 free by the rupture of the enclosing mem- 

 brane as a gonidium which can at once 

 germinate (Mann & Hutchinson, '07). 



Isogametes are known to occur in a 

 number of different forms. In Cephalearos 

 and Phycopeltis they arise from disc-cells, 

 but in Trentepohlia the gametangia are 

 found in terminal or intercalary positions 

 on the erect branches, either solitary or in 

 groups; they are very similar to the zoogo- 

 nidangia, with which it is probable they 

 are often confused. The gametes are 

 biciliated, ovoid and complanate, without 

 a pigment-spot (fig. 92 B). They are set 

 free from the gametangia in large num- 

 bers and their fusion has been observed 

 in Trentepohlia and Phycopeltis. The 

 germination of the zygote is not fully 

 known, but is probably direct. Gametes 

 have occasionally been observed to ger- 

 minate parthenogenetically. 



Fig. 202. Apices of three branches of 

 Trentepohlia aurea (L.) Mart. A, shows 

 a very irregular and much elongated cap 

 (ap. cp.). B, apical cell with a laterally 

 displaced apical cap. G, end of branch 

 showing three successively displaced 

 apical caps (da 1 , da 2 , da 3 ), x 800 (after 

 West & Hood). 



The genera are : Trentepohlia Martins, 1817 [ = Chroolepus Agardh, 1824 ; Nylandera 

 Harlot, 1889]; Phycopeltis Millardet, 1870 [ = Phyllactidium Kiitzing, 1849 (in part); 

 Chromopeltis Keinsch, 1875; Hansgirgia De Toni, 1889]; Cephaleuros Kunze, 1828 

 [ = Mycoidea Cunningham, 1878 ; Phylloplax Schmidle, 1898 ; Weneda Eaciborski, 1900]. 



The relationships of the three recognized genera were first clearly demonstrated by 

 Karsten ('91). Hariot separated 'Nylandera'' from Trentepohlia owing to the fact that 

 certain cells developed hairs, but this character can have no generic value when it is found 

 that some species of both Cephaleuros and Phycopeltis constantly develop hairs whereas 

 others are quite destitute of them. 



The genera Phycopeltis and Cephaleuros are epiphyllous and are almost exclusively 

 confined to damp tropical countries, whereas those species of Trentepohlia which occur on 

 rocks and stones and on the bark of trees are abundant in damp temperate regions and 

 extend far north in Scandinavia. Trentepohlia aurea (L.) Mart, is the most widely dis- 

 tributed and conspicuous species in western Europe, often forming large orange-red patches 

 on rocks. T. jolithus (L.) Wittr. gives off an odour of violets when moistened. The only 

 true discoidal type native to Europe is Phycopeltis epiphyton Mill. (fig. 203 A O), which 

 has been found as an epiphyte on the leaves of Abies pectinata, Hedera Helix and Rubus sp. 

 The species of Phycopeltis and Cephaleuros occur mostly in the damp tropical and sub- 

 tropical forests of both the New and Old Worlds. 



