32 A TEXT-BOOK OF BOTANY. 



is attached to rocks by means of a slender hold- fast. The thallus 

 is dichotomously branching, somewhat flattened, but may be quite 

 linear. The fronds show a mucilaginous modification of the cell- 

 walls. In the upper segments occur small differentiated areas, 



FIG. 15. Specimen of Chondrus crispus still attached to the rock where it was found 

 growing along the Massachusetts coast. 



sometimes called sori, of a more or less elliptical outline, which 

 on sectioning are found to be in the nature of sporangia, contain- 

 ing numerous tetraspores (Fig. 16). The spores are discharged 

 through narrow canals extending through the more or less com- 

 pact outer layer of the frond. The article found in commerce has 

 the color removed by being bleached through the action of the sun 



