PHYTOFLAGELLATES 123 



transverse diaphragm, but this appears to be traversed by a 

 peculiar short cylinder, about 70 m^ in diameter by 120 m/x long, 

 with a thin dense wall, occupying the center of the flagellum. The 

 two central fibers arise immediately distal to the cylinder and do 

 not appear to be attached to it. Projecting from the anterior faces 

 of the fused kinetosomes is a dense material in the form of a 

 cone-shaped chamber with a low-density lumen. 



Gibbs, Lewin, and Philpott studied series of cells fixed at 

 intervals after adhesion of mating pairs and found that within 

 10 minutes a bridge of homogeneous protoplasm connected the 

 apical papillae of the two cells. A factor suppressing the motility 

 of one of the mating partners is known to be passed through such 

 a bridge. After one hour, a dense core appeared within the 

 bridge, continuous with the anterior projections from the kineto- 

 somes in each cell. Flagella of mutant strains of Chlamydomonas 

 with impaired motility were studied by the same authors ; except 

 for decreased length in some paralyzed strains, the flagella all 

 were normal morphologically. 



Chloroplasts of C. reinbardi show the discontinuous stacks of 

 lamellar discs described in Chapter 2. The central pyrenoid is 

 traversed by tubules continuous with lamellar membranes and is 

 surrounded by starch plates (Fig. 7, PI. II). Starch appears first 

 around the pyrenoid but may subsequently be deposited else- 

 where in the plastid. Mitochondrial membranes resemble cristae 

 more than tubules, but often seem to have the shape of irregularly 

 oriented flat discs. Several compact stacks of Golgi lamellae with 

 peripheral microvesicles occur near the nucleus. Granular mem- 

 branes are well distributed through the cytoplasm, showing 

 occasional continuity with the outer membrane of the nuclear 

 envelope and with Golgi membranes. Larger empty vesicles 

 with smooth membranes are seen, some possibly representing the 

 contractile vacuoles but lacking a differentiated cortex. 



Electron-microscope studies on other, non-flagellated green 

 algae have been concerned mainly with chloroplast structure and 

 provide little additional information relevant to our consideration 

 of phytomonads. In general, chloroplasts resemble those of 

 Chlamydomonas, Golgi bodies appear in the vicinity of the nucleus, 

 and mitochondria have sparse, irregular cristae. 



