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 
Neegeli seytonemine, 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 Homocystew and 
Chroococcacee are absent from the Heterocystew. 
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 
Cyanophycee. 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 hematoxy- 
lene. Its form, however, is not definitely limited 
