31 



appear to constitute an axis (which is called a pseud- 

 axis or sympodium) on which the weaker branches 

 appear as lateral branches, the successive bifurca- 

 tions are alternately right and left, and so form a 

 scorpioid dichotomy. The growth is brought about 

 by a group of cells at the apex, called primary 

 meristem, this lies in a depression, and is not differen- 

 tiated. (In other cryptogams it is usually brought 

 about by a single cell). 



GENERAL ANATOMY. 



The tissue consists at the surface of small cells, 

 next to this it is laxer, and the midrib consists of 

 thickened elongated cells. 



The cell wall consists of two distinct layers, an 

 inner thin firm one, and an outer gelatinous one 

 (capable of swelling greatly in water) which 

 fills up the interstices of the cells, and has 

 the appearance of a structureless substance ; this is 

 the cause of the slimy character which the FucacecB 

 assume after lying in fresh water. The granular 

 contents appear to be mostly brown, but contain 

 chlorophyll which is concealed by other colouring 

 matters. The colour bodies are known as Plmophyll 

 grains, and vvhen treated with alcohol yield an olive- 

 green extract ; this extract when shaken up with, 

 double its volume of Benzine, and allowed to settle, 

 produces an upper green layer containing the 

 chloropliyll, while th« lower alcoholic layer is yellow, 

 and contains Phycoxantheine. 



