80 



PLANT-LIFE 



s p: 



sp. 



attached to larger seaweeds between tide-marks. The 

 whole plant ranges from 6 to 18 inches in length; it is 

 very abundant. The individual cells possess a single 

 nucleus and a number of chloroplasts masked with the 

 brown pigment. 



Ectocarpus produces two distinct kinds of reproduc- 

 tive organs, which are called " sporangia " (spore-cases). 

 Both kinds may occur on the same 

 plant, but it is usual for them to 

 develop separately on different indi- 

 viduals ; they arise, like branches, 

 from the side of the filament. In 

 Pig. 26 we have a drawing of the 

 simpler kind of sporangia as seen 

 under the microscope. Each sporan- 

 gium is a single pear-shaped or 

 spherical cell packed with protoplasm, 

 which ultimately divides and gives 

 rise to numerous zoospores. The 

 FIG. 26. SPORANGIA zoospores of this genus, as in all the 

 Sl^T B~ Alg, are furnished with a 

 FILAMENT OF EC- pair of cilia which emerge from the 



x^ocT 8 VATUS ' side > not the a P ex of the cel1 ' When 

 they are in motion one cilium points 



in the direction of progress and the other trails behind. 

 In due time the zoospores escape from the sporangium 

 and swim about. They come to rest after a period 

 of activity, and produce new plants. 



The second kind of sporangium (see Fig. 27) is com- 

 posed of many cells in which motile gametes are de- 

 veloped. Each one of these, like the asexual zoospore, 

 bears two cilia inserted laterally. In E. siliculosus it 



