152 THE ALGAE 



basal disc and are usually devoid of terminal hairs. There are also 

 occasional sheathed hairs with a basal meristem and a terminal hair 

 with the normal intercalary meristem. These also form medullary 

 threads. Some of the upper cells become meristematic and produce 

 lateral assimilators (Fig. 82D) and sheathed hairs. Further laterals 

 are produced from growth of the cell beneath these hairs, one or 

 other of the laterals assimiing a terminal position. In this way the 

 axial threads are built up of successive basal portions of laterals, 

 the apical portions of which become the cortex and subcortex. 

 This sympodial type of branching is in contrast to the monopodial 

 branching of the axial thread of Mesogloia. Supplementary medul- 

 lary threads, with secondary laterals, are formed by down-growing 

 threads from the basal cells of the primary laterals. Branching 

 hyphae may grow out from any cell. 



The cortex is composed of club-shaped primary and secondary 

 assimilatory hairs arranged either singly or in falcate tufts. The 

 unilocular sporangia develop as outgrowths from the basal cells of 

 the primary assimilatory filaments, whilst the plurilocular spor- 

 angia appear in secimd rows on the outermost cells of the same 

 type of filament. The zooids from the unilocular sporangia ger- 

 minate immediately, or else some considerable time may elapse, 

 perhaps as much as three years according to some observers, before 

 any development takes place. They give rise to a microscopic 

 plethysmothallus on which plurilocular gametangia similar to those 

 of Mesogloia are to be found. After zooids have been liberated from 

 the plurilocular sporangia of the plethysmothallus yotmg macro- 

 scopic Eudesme plants appear, so that it may be assumed that there 

 is a definite alternation of generations in which the small gameto- 

 phyte forms the winter phase. Other genera with a similar structure 

 include Myriogloia and Tinocladia. 



Chordariaceae : Chordaria (a small cord). Fig. 83 



In Mesogloia there is a single central filament whilst in Eudesme 

 there are several, but in Chordaria development has proceeded a 

 stage farther and the branched cartilaginous fronds possess a firm, 

 pseudo-parenchymatous medulla of closely packed cells that have 

 become elongated in a longitudinal direction. The cortex is com- 

 posed of crowded, radiating, assimilatory filaments, which are 

 either simple or branched, the whole being embedded in a thick 

 layer of jelly, thus giving the plant a slimy touch. This type of 



