80 



FLORIDE^!. 



whole plant adopts a coral-like appearance. Other genera which 

 are similarly incrusted, and have a leaf-like or even crustaceous 

 thallus (such as Melol>esia, Lithothamnion), are included in this 

 family. 



In some instances the cells of the thallus may be found differ- 

 entiated into more or less well defined tissues, so that it is possible 

 to find special assimilating, mechanical, and conducting tissues, 

 the last named in some cases having the double function of con- 

 ducting and of serving as a reservoir in which starch is found as a 

 reserve material. The cells of the Floridese, which are formed by 

 the division of a mother-cell into two daughter-cells of unequal 



FIG. 75. Ccramium diaplianum (uat. size). 



FIG. 76. Delesseria sanguinea (about 



size, have always larger or smaller pits in the cell-walls, and the 

 thin cell- wall separating two pits from each other is perforated by 

 a number of small holes. These pits are particularly developed in 

 the conducting tissues, but sieve-tubes are very rarely to be found. 



Tetraspores may be wanting (e.g. Lemanea) or may often arise 

 on special, non-sexual individuals. In some (e.g. Bntrachospir- 

 mum) only one tetraspore is formed in each tetrasporangium, but 

 the number is generally four, which may be formed tetrahedrally 

 (Fig. 73) or by divisional walls perpendicular to each other, or 

 even in a single row. The tetrasporangia in some species are free 

 (Fig. 73), but in the majority they are embedded in the thallns. 



The sexual reproduction (discovered by Thuret and Bornet, 



