28 OUTLINES OF PLANT LIFE. 



the ebbing tide ; the hair pits are useless, so far as known ; 

 and the strong, elastic disk and stalk above hold the plants in 

 place as they sway constantly back and forth in every wave 

 of the risirig or falling tide. 



38. Color, — The coloring matter in Fucus and other brown 

 seaweeds is of two kinds, a green (chlorophyll), and a brown. 

 These colors are found chiefly in the cortex, which is, there- 

 fore, the food-making tissue (see ^ 190), while the internal 

 tissues may be used for storage of reserve food. 



EXERCISE VII. 



Bladder Wrack. {Fucus vesiculosus). — Place a plant in a glass dish or 

 a pan of water. Observe 



1. The general form of the body or thallus ; its mode of branching. 



(H 34-) 



2. The thicker central region forming a midrib, with thinner wings. 

 (Figs. 27, 28.) 



3. Downwards, the thickening of rib and death of wings to form slalk 

 near base. 



4. The lobed attachment disk at base of stalk. 



5. The swollen regions of the wings here and there. Cut into one of 

 these and observe that it is a bladder. 



6. The notched tips of some branches ; the enlarged and more or less 

 distorted tips of most, forming the receptacles. 



7. Scattered on the thallus minute elevations, from which protrude 

 through an opening at the top a tuft of fine hairs. These are the mouths of 

 the hair pits. (Fig. 28.) 



8. Crowded on the receptacles, larger warts with a hole at top and sim- 

 ilar protruding hairs. These are the months of larger pits, conceptacles, 

 which contain the sex-organs. 



Cut two thin transverse sections of the thallus, one through the bladder 

 and the other through the general thallus. The latter should include a 

 hair pit. Examine them with a lens and observe 



9. In the latter, the denser outer tissues; the cortical region ; the looser 

 inner ones, of elongated threads and much mucilage, the medullary region; 

 the thicker denser midrib ; the form of the hair pit. 



10. Note the difference between the structure of the bladder and the 

 unswoUen wing. Which region is altered to form the bladder ? 



