THE ALG^E. 113 



seen in sections through these enlargements as orange- 

 yellow masses ; the oogonia are borne either in the same 

 cavities or in cavities on other plants. The eggs that 

 develop in the oogonia are set free into the water, and 

 the flagellated antherozoids, liberated from the antheridia, 

 find and fertilize them. This, at least, is the belief ; but 

 the actual entrance of the zoospore into the egg has never 

 been observed. After fertilization, the egg secretes a wall 

 about itself, enlarges, attaches itself to some fixed support, 

 and grows into a fully developed plant. 



FUCUS VESICULOSUS. PRACTICAL STUDIES. 



Fucus vesiculosus, or Bladder Wrack, is the most widely 

 distributed of the Rockweeds. The frond or thallus is 

 wide and flat. The air sacs, which are conspicuous, are 

 arranged in pairs on the distinctly dichotomously divid- 

 ing frond. (Fig. 61, (7andD.) 



1. Observe, if possible, the plants growing in their 

 natural positions attached to the rocks. Draw an entire 

 plant, labeling the attachment disk, stipe, frond, midrib, 

 air sacs, and the enlarged ends of branches which bear 

 the conceptacles containing sexual reproductive organs. 



2. Thoroughly dry and pulverize some of the Rock- 

 weed, and place it in cold fresh water. The water soon 

 takes on a brownish color, due to the special pigments 

 which give the brown and olive colors to the plant. 



Place pieces of fresh Rockweed in alcohol. The alcohol 

 dissolves the chlorophyl and assumes a yellowish-green 

 color. 



3. Place a piece of the frond that has been preserved 

 in alcohol between two pieces of pith and cut thin trans- 

 verse sections. Mount in glycerine. Notice the differ- 

 ences between the centrally situated medullary cells and 

 the cortical cells. Can you make out an epidermis ? The 



CLARK'S BOX. 8 



