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Practical Plant Biology. 



symmetrical arrangement confer on this branch an architecture 

 which is strikingly beautiful. 



The walls of these cells are comparatively thick, and against 

 their inner surface is the usual layer of cytoplasm containing 

 one or more small nuclei (invisible till stained) and countless 

 chromatophores. These latter are very minute and so closely 

 packed together that the cytoplasm appears almost uniformly 

 coloured with them. They have a rose colour, due apparently 

 to an intense red pigment, which completely masks the presence 

 of a green colouring substance. This latter is plainly seen when 



FIG. 20. Polysiphonia fastigiata, branch above on left, sketch drawn when 

 microscope is locussed on the near side, on the right, when the focus is 

 transferred to the median plane ; below is a reconstructed transverse 

 section. All x 150. c, cortical cell ; m, medullary cell. 



the red pigment is removed by alcohol or hot water. The green 

 colour is due to the presence of chlorophyll, possibly in its two 

 forms a and b together ; very probably with a certain amount of 

 xanthophyll and carotin. In the cytoplasm are also often seen 

 granules of a substance resembling starch and crystals of protein. 

 The contents of the axial cells resemble those of the cortical 

 cells save that the chromatophores are not so densely crowded 

 in their cytoplasm. 



As we pass in the examination of one of the branches of 



