386 



BOTANY 



PART II 



CLASS V 

 Dinoflagellatae ( l > n > 17 ' 19 ) 



The Peridineae or Dinoflagellatae are connected as an independent 

 and further developed group with certain Flagellata. They occur as 

 unicellular, free-swimming organisms in fresh 

 water, but for the most part in the sea, where, 

 together with the Diatomeae, they constitute 

 an important constituent of the phyto-plank- 

 ton. Their cells are characterised by the pos- 

 session of two long cilia or flagella which 

 spring from the middle of the ventral surface 

 in a longitudinal furrow ; one of the cilia is 

 directed backwards, the other is thrown 

 into curves and lies in a transverse furrow 

 (Fig. 316). The protoplast contains a nucleus, 

 vacuoles of different sorts, and numerous 

 brownish-yellow chromatophores ; the latter 

 contain a mixture of several pigments. Starch 

 or oil is formed as the product of assimilation. 

 While the Gymnodiniaceae (Fig. 317 d) 

 have either naked cells or cells limited by 

 a uniformly thickened cellulose wall, the 



typical Peridiniaceae have a wall composed of cellulose formed of 

 polygonal plates ; these are usually delicately sculptured and per- 



PIG. 316. Peridinium tabulatum. 

 (After SCHILLING.) 



FIG. Zl7.Cystodinium Steinii : a, cyst ; b, division into two swarm cells ; c, a cyst swelling ; 

 d, liberated swarm cell. ( x 480. After KLEBS.) 



forated with pores. The transverse furrow is formed by one girdle- 

 shaped plate (Fig. 316). 



In many Peridineae of the plankton the plates bear special wing-like expansions 



