252 



F. BORGESEN 



Fi 



The rhizoids grow out from the lower- 

 most ends of the cells in the basal part of 

 the plant (Fig. 4 b). They are irregularly 

 bent and have thick walls. They grow down- 

 wards along the wall of the main cells and 

 contribute highly to the strengthening of these. 

 Reaching the host plant they become divided 

 in several thinner filaments which are termin- 

 ated by irregular coralliform lobes. I have 

 not seen any cross walls in these rhizoids. 

 From the base of the main cells even high 

 up in the thallus such rhizoids are formed. 



The growth of the plant is acropetal. 

 The young cells are at first seen as small 

 outgrowths upon the end of the mother-cell. 

 These outgrowths are often rather large before 

 they become separated by a wall (comp. 

 Fig. 3). The ramification always takes place 

 in the same plane. 



When the apex of a cell touches the 

 neighbour branch it becomes fastened to it 

 by a thick cellulose ring, formed in the same 

 way as in Microdictyon umbilicatum (Fig. 4 a). 



The large cells are about 200 [i wide 

 and as much as 600 \x long. The cells contain 

 a wall plasma with numerous chromatophores 

 Young plant of Rhifcdiphyllon forming a dense network. Numerous pyrenoids 

 reticulatum (Asken.) Heydr., c. B0 /i. are regularly distributed in the chromatophores. 



Fig. 4. RJiifiidipJiyUon reticulatum (Asken.) Heydr. a summit of plant, c. 60 /i; b base of small 



specimen, c. 30 /i. 



