360 



(Fig. 354). These are, as a rule, developed from the narrowings of 

 the thallus and consist of a short stalk ending in a broad disc. As the 

 specific name indicates the shape of the thallus reminds one very 

 much of that of Opuntia, being rather regularly narrowed and again 

 enlarged, giving it a resemblance to a chain whose single joints are 

 elongated elliptic. From the thickest part of the joints, which is 



Fig. 354. Catenella Opuntia (G. et W.) Grev. 



Parts of plants, a, from below; b, from the side. 



(About 6:1). 



found frequently somewhat above the middle of the joint, one or 

 commonly two opposite side-branches grow out, these sometimes be- 

 ing erect, and sometimes bending downwards in different directions 

 and fixed by haptera to the mangrove roots. By this way of growing 

 a felted cover about 2 cms high is produced round the roots. 



From transverse and longitudinal sections of the thallus (com p. 

 OKAMURA, Icones, vol.1, pi. 39) it appears that the tissue in the middle 

 consists of several thick-walled filaments running the length of the 

 plant and composed of rather long, cylindrical cells. From these cells thin 

 filaments are given off in all directions towards the periphery, being 

 bi-or tripartited several times, forming a very lacunose tissue. Near the 

 periphery the filaments are much ramified, their cells becoming smaller 

 and densely packed, forming in this way a firm cortical layer. 



