552 Annals of the South African Museum. 



nucleus in F. Rousseletii and F. capensis is apparently a good deal 

 larger. 



(ii) The Chloroplast. Each cell contains a single large chloroplast 

 consisting of (1) a massive, saucer-shaped portion filling the broad base 

 of the plastid and extending into the protoplasmic connecting strands, 

 and (2) a broad, strap-shaped portion which extends from the basal 

 part of the cell right up the dorsal side to the apex, sometimes even 

 beyond it and a little way down the ventral side. Usually there is 

 only one such extension, but occasionally one or two smaller processes 

 extend upwards from the base, almost enclosing the central colourless 

 portion ; this is, however, rare except in very young cells. In shape, 

 then, the chloroplast may be compared to a thick-bottomed cup with 

 a large piece broken away in the front half. As the cell ages, the 

 chloroplast becomes much less clearly defined and considerably 

 smaller, no longer extending into the protoplasmic connections. 

 When young the whole chloroplast is saturated with chlorophyll of 

 a clear, vivid green colour ; with age the colour becomes much lighter. 



From the above description and from the figures (fig. 1, A-D) it 

 will be seen that the form of the chloroplast differs considerably 

 from that shown by Janet (1912, p. 45, fig. 6) for V. globator, par- 

 ticularly as regards the posterior elongation here the latter is 

 definitely extended right up into the apex of the cell, where it is in 

 connection with the cilia, whereas in F. globator Janet shows the 

 chloroplast as saucer-shaped, the back only slightly higher than the 

 front and not reaching the apex. 



(iii) The Pyrenoid. In the development of the gonidium, after 

 the last cell-division prior to inversion, as a general rule each cell 

 contains a single pyrenoid. Occasionally vegetative cells with two 

 pyrenoids are seen, but as a rule when cells with more than one 

 pyrenoid are found they are probably not somatic cells but young 

 reproductive cells (most often male) which have not yet developed 

 beyond the first stage in differentiation (fig. 1, G). 



The pyrenoid is embedded more or less centrally in the massive 

 basal portion of the chloroplast. In life the structure shows a dense 

 central portion surrounded by a lighter zone. Starch is formed in 

 rods, platelets, or more irregularly shaped masses on the outside of 

 the central mass. Stained with iodine, these slabs of starch show 

 very clearly, varying from two to five per pyrenoid, four being a 

 common number in mature cells, giving the pyrenoid a cruciform 

 appearance when stained (fig. 1, H). 



It is a moot point as to whether the pyrenoids arise always from 



