THE ALG^E 



191 



brown colour. This superficial layer is no doubt the 

 chief assimilating tissue. Within this we come to large 

 parenchymatous cells, less deeply coloured, and as we 

 approach the middle of the thallus the cells become 

 elongated (cf. Fig. 82). In the lower part of the plant the 

 elongation of the central cells is so extreme that they 



Fro. 81. Pdvetia canaliculata. A, small fertile plant; d, 

 attaching disc ; r, r, receptacles, each of which bears a 

 number of wart-like conceptacles. of natural size. B, 

 transverse section of a receptacle, passing through several 

 conceptacles (c). Magnified about 4. (After Thuret and 

 Bornet.) 



form a tangled web of branched filaments or liyplue. 

 The elongated cells appear to serve the purpose of 

 conducting food-substances, for they possess regular 

 sieve-plates perforated like those of the vascular plants. 

 Such sieve-plates occur both in the transverse and 

 longitudinal walls of the long cells. The hyphae of the 



