I.— IXTRODUCTIOX. 



The Rhodophyceae are a very distiuctive class in tlie 

 Eupliycese or Algse, wliicli form a sub-division of tlie 

 Thallophyta. They are separated from tlie otlier classes 

 of the Eiiphycere by their reddish or violet colour. This 

 colour is produced by tbe green chlorophyll being obscured 

 by a red colouring matter, called Phycoerythrin. The 

 RHonoi'iiYCKA.ic embrace two su])-classes, namely, the 

 ]?AXGiALES and the Floride.e. The representatives of the 

 former have very simple and undiiferentiated filamentous 

 or membranous multicellular bodies. The sexual organs 

 are extremely simple. The Florideae have multicellular 

 bodies, consisting usually of much-branched rows of cells, 

 which often form plants of good size and firm structure. 



To the sub-class Floridese belongs the subject of this 

 memoir, Chondrus crii^pus, the Irish Moss. With the 

 exception of nine genera, five of which are confined to 

 freshwater, the Floridese are exclusively marine plants. 



The arrangement of the natural orders of the Floridere 

 into series is dependent on the various methods by which 

 the fruit develops after the fertilisation of the female 

 organ. It is unnecessary to refer to the subject in detail 

 here. It must suffice to say tliat the natural orders are 

 arranged in four series, namely, the Nemalionales, the 

 Gigartiiiales, the lihodymeniales and the Cryptonemiales. 



The natural order to which Chondrus belongs is that 

 of the Gigartinacepe, one of the Gigarlinales. The only 

 other order of this series, the Acrotylaceae, differs from 

 the Gigartinacese in the arrangement of the asexual spores 

 in their mothercell. The tetraspores of the latter are 

 formed by cruciate, those of the former by zonate, 

 division. 



