THE BIONOMICS OF CONVOLUTA EOSCOFFENSIS. 391 



granular substance, soluble in distilled water, but insoluble 

 in absolute alcohol, occur round the nucleus. 



We have now to trace the development of these green cells 

 from their colourless predecessors. In doing this it is neces- 

 sary to consider the latter in more detail than in the last 

 section. We therefore begin our description with the 

 appearance of the colourless cells of the recently hatched 

 Convoluta. 



The simplest form of colourless cell is spherical, measuring 

 •006 — "Ol mm. in diameter, and consists of a clear substance 

 and delicate wall, which does not give a cellulose reaction. In 

 fact, such cells resemble nothing so much as a vacuole with a 

 refractive enclosing membrane. More usually within the 

 " vacuole " there are one or more inclusions of a highly 

 refringent character. Sometimes the inclusions are divisible 

 into several marginal ones pressed against the membrane, 

 and one or more central bodies (PI. 81, fig. 14). More usually 

 irregular, curved, more or less comma-shaped inclusions occur 

 massed together at one pole of the cell (PL 31, fig. 12, Chr.) ; 

 and again, a mass of fine but highly refringent spherical 

 granules may take their place. The occurrence of starch is no 

 less inconstant than the form of the inclusions. In some 

 cases (PI. 31, fig. 8) starch can be detected with the utmost 

 clearness in each of the marginal and central bodies, though 

 these have as yet no colour. In such cases true leucoplasts, 

 with an amount of carotin too slight to cause recognisable 

 coloration, must be present. In the majority of cases, 

 however, no starch can be detected by the most careful 

 manipulation of the iodine reagents. It is therefore doubtful 

 whether the irregular inclusions are leucoplasts devoid of 

 starch or are protein crystals. 



The development of the chloroplasts is, again, a variable 

 one. In those cases iu which marginal starch-holding leu- 

 coplasts are present, a yellow pigment appears in each. In 

 other cases a green envelope gradually encloses the inclusions. 

 The latter is certainly the more usual method. Long after 

 the single chloroplast has acquired its full green colour the 



