FLORIDE& 



195 



(Lmx.), and a few other genera, the 'frond' becomes densely incrusted 

 by a deposit of calcium carbonate, giving to the so-called 'coralline's' 

 the external form and appearance of miniature corals. 



The ordinary non-sexual propagative organs of the Florideae are 

 bright red motionless spores, commonly formed in fours in the mother- 

 cell, and hence known as tetraspores (the sphaerospores of Agardh), and 

 the cell in which they are produced as a tetrasporange. The four spores 

 are sometimes arranged in a row, when they are called zonate ; more 

 often as quadrants of a sphere, when they are cruciate : rarely there are 

 only one or two, or occasionally eight. In the Ulvaceae, Lemaneaceae, 



FIG. T.-j2.Crouania attemtata Ag. , branch (x 40) ; B, apex of branch (x 100) ; c, lower ; 

 portion of branch with tetrasporanges ( x 100). (After Kiitzing.) 



and in some Nemalieae they are altogether wanting. The tetraspores 

 (see fig. 231) may be formed in the six following ways : (i) The 

 whole contents of the sporange become a single spore ; (2) the contents 

 divide into two equal parts by a transverse wall ; (3) they divide into 

 four quadrants by two successive bipartitions ; (4) they divide into four 

 tetrahedra by simultaneous quadripartition ; (5) they divide into four 

 by three parallel transverse walls ; (6) the contents divide into more 

 than four spores. On germination the tetraspores may give birth either 

 to sexual or to non-sexual individuals. In the monosiphonous Florideae 

 the tetrasporanges are usually formed at the expense of the ultimate 

 branchlets. In other forms they are most commonly found scattered 



o 2 



