SECT. II. 



ULVA. 



225 



The "Divas, which are the grass green lavers seen on 

 all our coasts, originate in the simple vegetable cell, 

 whatever form their foliaceous fronds may ultimately 

 assume. When the cell is divided in one direction only, 

 a confervoid filament is the result ; and if the filament 

 should increase in breadth as well as length, according 

 to a determinate law, a ribbon-shaped frond may be 

 produced ; but when the original cell is divided into four 

 cells, and each of these four and all their successors 





Fig. 22. TJlva latissima : a, portion of ordinary frond ; 6, cells in which the endochrome 

 is beginning to break np ; c, cells from the boundary between the coloured and colour- 

 less portion, some containing zoospores ; d, ciliated zoospores ; e, development of zoo- 

 spores. 



undergo similar division, the increase being as the 

 series 1, 4, 16, 64, &c., a membranous expansion is 

 formed, in which all the cells are firmly attached to 

 one another, and every portion is the exact counterpart 

 of another. The cells of the Ulvas frequently exhibit 

 an imperfect separation of the granular endochrome 

 into four parts preparatory to multiplication by double 

 division, and the entire frond or leaf shows the groups 

 VOL. i. Q 



