588 



PROGRESSIVE STAGES IN COMPLEXITY OF STRUCTURE. 



Usually only the portions serving for reproduction exhibit differences of shape, and 

 these are so subordinate in number and extent that the appearance of the whole is 

 very little altered whether they are present or not. It is of more importance with 

 regard to the general appearance, that most of the simple tissues enumerated, 





Fig. 139. — Laminarias in the North Sea. 



multiply and divide without the portions thus produced becoming separate or 

 detached. The nets of Hydrodictyon indeed multiply by the formation of 

 daughter-nets within single cells, which then become detached from the parent 

 plant. The disc-shaped plates of Pediastrum also multiply in a similar manner, and 

 in this sort of plant whole swarms of cell-complexes are always developed, so that 



