6o A TEXTBOOK OF THEORETICAL BOTANY 



colour. This is due to the presence of a carotinoid red pigment, haemato- 

 chrome, which masks the green colour of the chlorophyll. The actual colour 



FLAGELLA 



CONTRACTILE 

 VACUOLE 



PSEUDOPODIA 



NUCLEUS 

 CHLOROPLAST 



HAEMATOCHROME 

 GRANULES 



PYRENOID 



INNER 

 CELL 

 MEMBRANE 



OUTER 



CELL 



MEMBRANE 



PSEUDOPODIUM 



F'G. 2S-—fioematococcus pluvialis. A, Diagram showing the complete structure of 

 the vegetative cell. B, Posterior portion of a cell, enlarged to show the details 

 of the wall structure. {After Pascher.) 



of any particular cell depends upon the relative proportion of haematochrome 

 present, which in turn depends on the supply of nitrogen compounds. The 

 Alga very readily forms cysts by the withdrawal of the flagella and the 

 rounding up of the cell, in fact it is in this condition that the organism is 

 generally seen. 



