PHYTOFLAGELLATES 121 



kinetosome complex marks the morphological anterior pole of 

 the cell, and that Pedinomonas simply spends most of its time 

 swimming backwards. 



The flagellum of P. tuberculata bears a liberal garniture of 

 extremely fine mastigonemes, more flexuous and much more 

 delicate in appearance than those on the chrysomonad pantoneme 

 flagellum, and quite dissimilar to the stout, short mastigonemes 

 of Micromonas squamata. 



Another green alga with distinct mastigonemes is the quadri- 

 flagellate Platymonas. An unidentified species of this genus was 

 studied briefly by Pitelka and Schooley (1955) and subsequently 

 four strains of P. subcordiformis were surveyed by Pitelka and 

 Lewin (Lewin, 1958). In all instances, all four flagella bear fairly 

 abundant but (in the dried specimens seen) erratically distributed 

 and oriented mastigonemes (Fig. 41, PL XI). Although phyto- 

 monad affinities of Platjmonas have not been seriously questioned, 

 Lewin (1958) has shown that the cell wall contains polysaccharides, 

 not cellulose, and has suggested that a critical analysis of pigment 

 composition is to be desired. Haematococcus pluvialis (Sphaerella 

 lacustris) in electron micrographs published by Miihlpfordt and 

 Peters (1951) showed a thick, dense pile of very short fibrils 

 surrounding the entire flagellum, even the tip. These did not 

 resemble mastigoneme structures in any other flagellate and may 

 have been artifacts. Pitelka (1949) reported smooth, simple 

 flagella in the same species. 



Other species of green algae studied with the electron micro- 

 scope have proved to have simple or acroneme flagella. The 

 spotty occurrence of mastigonemes in phytomonads and their 

 frequently disorderly appearance (an artifact?) when they are 

 present leaves wide open the question of their significance, both 

 functional and phylogenetic. 



The only other phytomonad flagellate genus for which 

 published reports on ultrastructure are available is Chlamydomonas. 

 C. reinhardi was examined in some detail by Sager and Palade 

 (1957), who were primarily interested in chloroplast structure, 

 and the flagellar apparatus of C. moewusii was studied by Gibbs, 

 Lewin, and Philpott (1958). The Chlamydomonas cell (Text-fig. 7) 

 is limited by a unit membrane and surrounded by a cellulose wall 

 that appears in electron micrographs as a homogeneous or 



