PHYTOFLAGELLATES 103 



organelle provided an extraordinarily adaptable means of 

 enhancing structural organization. 



Among the phytoflagellates, diversity and relationship are most 

 readily assessed biochemically; thus the kinds of photosynthetic 

 pigments, of products of photosynthesis, and of skeletal or wall 

 components are key taxonomic characters. Purely morphologic 

 features such as number and position of flagella and nuclear 

 cytology generally are less reliable though still often significant 

 indicators. Except for some remarkable surface specializations, 

 anatomy at the cellular level does not become as elaborate as it 

 does in the zooflagellates. The number of phytoflagellates 

 thoroughly investigated with the electron microscope is still so 

 small that we cannot say whether ultrastructural differences can 

 be correlated with biochemical peculiarities; nonetheless there 

 are a few promising clues. 



The phytoflagellates may be roughly divided into two large 

 assemblages, the brown stock and the green stock, characterized 

 by different sorts of pigments. Inviting lines of biochemical 

 research are suggested by speculations on the phylogenetic 

 relationships between and within these groups (see Hutner and 

 Provasoli, 1951; Dougherty and Allen, 1959, 1960). We shall 

 consider the brown stock first. Several important groups within 

 these assemblages have yet to be studied with the electron 

 microscope. 



Class Chrysomonadea 



The Chrysomonadea include many familiar and conspicuous 

 genera, some of which have been used widely in axenic culture 

 for biochemical studies. They also contribute importantly to the 

 indescribably huge numbers of cells that constitute the micro- 

 plankton of marine and fresh waters. Most of these are poorly 

 known because of their minute size and fragility. They escape 

 an ordinary plankton net, and only the most dedicated light 

 microscopists have been willing to bother with them at all. In a 

 notable series of recent studies, Parke, Manton and Clarke (1955— 

 1959) and Manton and Leedale (1961a, 1961b) have applied 

 combined techniques of light and electron microscopy to the 

 abundant marine planktonic species of the genus Chrysochromulina. 

 Thanks to this and other work, it is becoming apparent that the 



