MORPHOLOGY 79 



t ophores vary in form among different species ; namely, discoidal, 

 ovoid, band-form, rod-like, cup-like, network or irregularly dif- 

 fused. The color of the chromatophore depends upon the amount 

 and kinds of pigment which envelops the underlying chlorophyll 

 substance. Thus the chromatophores of Chrysomonadina are 

 brown or orange, as they contain one or more accessory pigments, 

 including phycochrysin, and those of Cryptomonadina are of 

 various types of brown with very diverse pigmentation. In Chla- 

 romonadina, the chromatophores are bright green, containing an 

 excess of xanthophyll. In dinoflagellates, they are dark yellow or 

 brown, because of the presence of pigments: carotin, phylloxan- 

 thin, and peridinin (Kylin), the last of which is said to give the 

 brown coloration. A few species of Gymnodinium contain blue- 

 green chromatophores for which phycocyanin is held to be re- 

 sponsible The chromatophores of Phytomonadina and Euglenoi- 

 dina are free from any pigmentation, and therefore green. Aside 

 from various pigments associated with the chromatophores, there 

 are carotinoid pigments which occur often outside the chrom- 

 atophores, and are collectively known as haematochrome. The 

 haematochrome occurs in Haematococcus pluvialis, Euglena 

 sanguinea, Chlamydomonas, etc. In Haematococcus, it increases 

 in volume and in intensity when there is a deficiency in phosphorus 

 and especially in nitrogen; and when nitrogen and phosphorus 

 are sufficiently present in the culture medium, the haematochrome 

 loses its color completely (Reichenow; Pringsheim). Steinecke also 

 noticed that the frequent yellow coloration of phytomonads in 

 moorland pools is due to a development of carotin in the chro- 

 matophores as a result of deficiency in nitrogen. 



In association with the chromatophores are found the pyre- 

 noids (Fig. 31) which are usually embedded in them. The pyre- 

 noid is a viscous structureless mass of protein (Czurda), and may 

 or may not be covered by tightly fitting starch-envelope, com- 

 posed of several pieces or grains which appear to grow by apposi- 

 tion of new material on the external surface. A pyrenoid divides 

 when it reaches a certain size, and also at the time of the division 

 of the organism in which it occurs. As to its function, it is gen- 

 erally agreed that the pyrenoid is concerned with the formation 

 of the starch and allied anabolic products of photosynthesis. 



Chromatophore-bearing Protozoa usually possess also a stigma 

 (Fig. 31) or eye-spot. The stigma may occur in exceptional cases 

 in colorless forms, as in Khawkinea according to Jahn. It is ordi- 



