250 SEAWEEDS 



Other colours, such as purple, reddish purple, violet, 

 yellow, and brown, are imparted to the plants by the 

 coloration of their gelatinous envelopes. This 

 colouring matter of the envelope has been called by 

 Nsegeli scytoneminc, and is sometimes to be seen in the 

 whole length of the sheath, sometimes only in part 

 of it, but the peripheral part is more strongly 

 tinged than the internal part, and it is displayed 

 most vividly on the parts most exposed to light. 

 The blue and red colours found in Homocystccc and 

 Chroococcacece are absent from the Hcterocystece. 



The colouring matter of the cells is not associated 

 with definite chromatophores, as has been reported 

 by several observers, the error having arisen from 

 the presence of crystalloid bodies, or from the fact 

 of the plant studied not being a member of the 

 Cyanophyc&B. The protoplasmic contents of the 

 cells are almost uniformly tinged with the colouring 

 matter. This colour differs somewhat with the age 

 of the plant and the degree of its exposure to light. 

 It is ordinarily more greenish in young fila- 

 ments with uncoloured envelopes, but with age 

 it becomes more olive or even yellow. As has been 

 pointed out by Bornet and Flahault, the other 

 colours, seen in the protoplasm of herbarium speci- 

 mens, are due to decomposition. No true nucleus 

 has been observed, though its discovery has been 

 reported by several observers. Zacharias and others 

 have shown that the error is due to the presence in 

 the centre of the cells of a colourless portion of 

 protoplasm, which may be stained with hsematoxy- 

 lene. Its form, however, is not definitely limited 



