Coleoch&tacesB 



315 



branches are all procumbent and in some species concrescent (C. sciitata, 

 C. orbicularis), in which case the thallus is a more or less parenchymatous 

 disc one layer of cells in thickness (fig. 207). In C. soluta the procumbent 

 filaments are not concrescent and the disc consists of branched filaments 

 radiating from a central point. In other species the ramification is not 

 confined to one plane (C. irregularis, C. pulvinata), but numerous ascending 

 branches are given off, the whole thallus sometimes forming a hemispherical 

 cushion. Growth is peripheral and due to the divisions of the terminal cells 

 of the branches, which in the discoidal forms are the marginal cells of the 

 disc. In some species the branching is apparently dichotomous, but in others 

 it much resembles that of Cladophora or Stigeoclonium. 



Some of the cells of the thallus are always furnished with sheathed 

 bristles. Each bristle is a long colourless hair issuing from a narrow 



Fig. 207. Coleochsete scutata Breb. x 100. 



cylindrical basal sheath (up to 50 //, in length). Pringsheim ('60) originally 

 described these bristles as jointed or septate ; and Lambert (10) has recently 

 asserted that, notwithstanding the fact that this articulation has not been 

 recognized by Jost ('95), Wille ('97), Chodat ('98), West ('04), Oltmanns ('04), 

 or Collins ('09), the bristles of some young Coleochtete-plants he examined 

 were distinctly articulate. It is not improbable, however, that this articu- 

 lation is only apparent, as in Aphanoch&te, and that the bristles are not 

 truly septate. Lambert found that the bristles attained a length of 

 4*5 rnm. 



The most curious species of the genus is C. Nitellarum Jost ('95 ; 

 Lewis, '07), which is endophytic in the outer layers of the wall of species 

 of Nitella. In consequence of its habit the cells are greatly flattened with 

 thin cell-walls ; they are also of a much more irregular shape than those of 

 any other species of the genus. 



