52 Clilorophycem 



as fuchsin, safranin, methylene-blue and gentian- violet. The outer 

 layers often become thick coats of mucilage by the formation of 

 series of pectose constituents which exhibit all stages between 

 insolubility and complete solubility in water. It is not merely a 

 hydration but a molecular change, and successive increments are 

 often added by the gelatinization of other layers of the cell-wall. 

 In some of the unicells the increase in thickness of the cell-wall 

 due to gelatinization is only on one side and elongated colonies 

 such as those of Hormotila are formed. 



The gelatinous pectose compounds although sometimes forming 

 a large proportion of the cell -wall, do not alternate with layers of 

 cellulose, but there appears to be a continual exudation of them 

 through the inner layers of cellulose, a mass of jelly being thus 

 formed on the outside of the cellulose wall. This is best seen in 

 some of the Protococcoidese and Conjugate. The mucilage in 

 which filaments of Algse are so frequently embedded exhibits a 

 distinct radiating fibrillar structure which is clearly brought out 

 by various reagents. The radiating structure of the enveloping 

 mucus has long been known in the Conjugates and has at times 

 given rise, especially in the Desmidiacea?, to grave morphological 

 misconceptions. 



The cell-walls of (Edogonium and other Alga? exhibit peculiari- 

 ties of structure which will be described in their respective families. 



Whatever the nature of the cell-wall one of its primary func- 

 tions is the regulation of osmotic changes. 



Hairs and bristles are developed by certain green Algae belong- 

 ing to the Coleocha3tacea?, Herposteiracese, CEdogoniaceas, Chseto- 

 phoracese and ChastopeltidaB. They are of many kinds, from 

 slender articulate branches such as the piliferous apices of Chceto- 

 phora, to exceedingly fine inarticulate hairs such as the seta^ of 

 Bulbochcete, Herposteiron, ChcBtosphceridium, or Gonochcete. 



The thallus often develops special root-like organs of attach- 

 ment or haptera (commonly termed rhizoids), but these are as a 

 rule only found in the young plants, most of the older ones occur- 

 ring as freely floating masses. 



The chromatophores are usually distinct, and in the forms with 

 a filamentous or expanded thallus they are frequently characteristic 

 of the different families or genera. They are of a bright green 

 colour due to the presence of chlorophyll and are therefore cJiloro- 

 plasts. Sometimes they are very difficult to define, but at other 



