288 



of rhizoids break out (comp. fig. 287). They issue from the fore- 

 most end of each cell. These rhizoids are often of considerable 

 length, up to 1mm or more, but seldom ramified. They have no 

 walls and do not generally end in a disc. Only a few have been 

 found with a rather irregular disc, like those described by AM- 

 BRONN, 1. c., p. 211. From the mother-cell the rhizoids are separated 



by an oblique wall. The cylindrical stem of 

 the rhizoids is about 30 /j. thick. 



Upon the dorsal side, the main stem 

 bears two kinds of branches, some with in- 

 definite growth able to grow out to a main 

 filament like the mother stem, and some 

 with limited growth. In the following we may 

 call them respectively branches and branch- 

 lets. 



The branches with continuous growth 

 are placed alternately on both sides of the 

 main stem, one upon each segment, and in 

 such a way that there in the typical form 

 are always three segments between those 

 bearing the branches (Fig. 287). 



Upon the upper dorsal side of these three 

 segments the branchlets with definite growth 

 issue. These are placed singly, that is, a 

 single one upon each segment, in two rows 

 and in such a way that after each branch 

 with continuous growth a branchlet is de- 

 veloped from the opposite side of the stem; 

 if this branch is found on the left side of 

 the stem, the following branchlet is placed 

 on its right side, the next one is then found on the left side and 

 the third again to the right, then follows a branch on the right 

 side and so on. AMBRONN, 1. c., pi. IV, fig. 17 and FALKENBERG, 

 1. c., p. 303 have given clear diagrams of the arrangement of the 

 branches and branchlets. 



At first the branchlets are much more developed than the 

 young branches. The young branchlets are much curved in the 

 opposite direction to that of the summit of the main stem, bending 

 down over the latter as a protecting cover (comp. fig. 287). 



The branchlets are never ramified; at their base they have 

 but few pericentral cells (4 5, comp. 288 a), upwards the number 



Fig. 288. Herposipho- 

 nia tenella(C. Ag.)Nagl. 

 , branchlet with te- 

 trasporangia. b, trans- 

 verse section of the 

 thallus. (a, about 90:1; 

 b, about 80:1). 



