PROTOZOA AS CELLS 21 



Lamellae appear more regularly oriented in a dinoflagellate 

 studied by Grell and Wohlfarth-Bottermann (1957) and in Euglena, 

 examined by Wolken (1956, 1959, 1960), Gibbs (1960), and other 

 workers (see citations in Chapter 4). Gibbs's detailed study shows 

 occasionally as many as 12 discs in a band, but most commonly 

 three. The bands are slightly sinuous on a small scale, but 

 generally traverse the entire plastid in parallel arrays (Fig. 6, PI. II), 

 the width of the granular chloroplast matrix between bands being 

 generally less than that of the bands. Where single discs end 

 within the band or meet the limiting membrane of the plastid 

 peripherally, a thickened rim is seen. 



An interesting apparent variation of this lamellar pattern occurs 

 in the chloroplast of the green algal flagellate Chlamydomonas 

 reinhardi (Sager and Palade, 1957; Sager, 1959). Here the discs 

 are imperfectly segregated into loose local stacks, which may be 

 oriented at different angles within one plastid. Some discs may 

 continue from one stack to another but many are restricted to a 

 single stack. A similar arrangement of discontinuous bands, 

 oriented circumferentially around a plastid that contains a large 

 central or eccentric pyrenoid, is seen in three other green algae 

 studied by Manton (1959a) and Manton and Parke (1960). This 

 sort of arrangement suggests an approach to the much more 

 rigidly ordered structure of the grana in chloroplasts of land plants. 

 Lamellae in the latter may extend for some distance through the 

 organelle, but local zones of compact piling, like stacks of coins, 

 include some discs limited to one particular stack or granum, and 

 account for most of the lamellar area at least in mature plastids. 



In Euglena (Wolken, 1956), bleaching of chlorophyll to pheo- 

 phytin is accompanied by breakdown of the lamellar structure. 

 The organelles swell or collapse, depending on the treatment used 

 to induce bleaching. Ghosts remain for some time, and upon 

 renewed exposure to light under normal conditions, lamellar 

 chloroplasts appear within a few hours. After prolonged periods 

 during which Euglena survives saprophytically, chloroplasts are 

 no longer recognizable in sectioned cells, and ultimately the cells 

 are unable to regenerate chlorophyll in the light. DeDeken- 

 Grenson (1960), however, working with centrifuged, dark-grown 

 Euglena that were incapable of regenerating chlorophyll, found a 

 particulate fraction containing yellow pigment. Sectioned pellets 



