DIRECTIONS FOR LABORATORY STUDY. 373 



5. On some plants observe that the smaller branches are 

 swollen here and there with more opaque contents at these 

 points. These are the tetrasporangia. Compare their size as they 

 are traced tip-wards. What do you infer as to their origin ? 



(IT 3*7. fig- 220) 



6. Demonstration. Mount tetrasporic branches and show the 

 tetraspores. 



The sexual reproduction is so specialized that beginners should 

 not be perplexed with it. (See p. 288.) 



H. BLADDER WRACK (Fucus vesiculosus}. 



Place plant in a glass dish or a pan of water. Observe 



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

 ing. (1[ 41.) 



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

 wings. (Figs. 42, 43.) 



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

 form stalk 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 pro- 

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

 are the mouths of the hair pits. 



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

 and similar protruding hairs. These are the mouths 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 unswollen wing. Which region is altered to form the 

 bladder ? 



Cut thin transverse sections through the center of the recepta- 



