Trentepohliaceae 305 



narrow and cylindrical, forming quite a contrast to the irregular outlines of 

 those situated in the peripheral region. 



The cells possess parietal chloroplasts, discoidal or band-like, with one 

 or more pyrenoids. In some cells of Gomontia up to five nuclei have been 

 detected, but this may have been due to the incipient formation of resting 

 akinetes. Starch is the usual food-reserve, with sometimes a fatty oil in the 

 rhizoids. 



Zoogonidangia are formed in the peripheral parts of the thallus by a 

 swelling of the vegetative cells, 2 4 zoogonidia arising from each mother- 

 cell in Gomontia, but many in Tellamia. The zoogonidia are ovoid, with 

 four cilia and a stigma. 



Resting akinetes occur in all the known species. They are formed from 

 ordinary vegetative cells in the peripheral parts of the thallus, and they grow 

 to a diameter of over 200 /i. They often become irregular in shape, their 

 walls increase in thickness, and independent rhizoids are developed (fig. 198 E}. 

 On germination they produce numbers of either aplanospores or biciliated 

 ' swarmers ' (gametes ?). 



The genera are : Gomontia Bornet & Flahault, 1888 ; Tellamia Batters, 1895 

 [=Foreliella Chodat, 1898]. Both genera include freshwater and marine species. 

 Tellamia perforans (Chodat) Wille penetrates into the shells of the common freshwater 

 mussel (Anodonta). 



Family Trentepohliaceae. 



The Algse of this family are the most completely subaerial of all the 

 Ulotrichales, many of them occurring in situations in which they have to 

 withstand much desiccation. They occur on rocks and stones, and as 

 epiphytes on the leaves and bark of trees. Some of the epiphytic forms 

 have also become parasites. 



The plants are filamentous and branched, forming in Trentepohlia felt- 

 like masses and tufts, but in Phycopeltis and Cephaleuros much more compact 

 discoidal thalli. In Trentepohlia there is a basal creeping portion of the 

 thallus, much less developed in some species than in others, from which 

 numerous erect, branched filaments arise. In Phycopeltis and Cephaleuros, 

 which are chiefly epiphytes on leaves, the basal part of the thallus is the 

 principal part of the Alga, erect branches being either entirely absent 

 (Phycopeltis spp.) or of the nature of multicellular hairs (Phycopeltis nigra 

 and certain species of Cephaleuros), In these genera the thallus is for the 

 most part discoidal, the disc consisting of concrescent branches with apical 

 growth. In Phycopeltis the disc is one layer of cells in thickness and entirely 

 epiphytic. In Cephaleuros it usually consists of more than one layer of cells, 

 and some species are parasites, numerous rhizoid-like branches penetrating 

 and destroying the tissue of the leaf. 



w. A. 20 



