288 THE BIOLOGY OF THE PLANT 



manner in which the midrib subdivides. Is it 

 regular ? Are all of the branches flattened in the 

 same plant ? Note at certain points on the thallus 

 of some of your specimens smooth swellings, the 

 vesicles. "Whereabouts on the thallus are these 

 most numerous ? Are they arranged in a definite 

 manner with regard to one another ? With regard 

 to the branching of the midrib ? Are they thick- 

 enings of the midrib or of the wing ? Pinch one 

 of these swellings between the thumb and the fin- 

 ger. Is the swelling hard or soft ? Can you easily 

 break it by pinching ? "With the razor cut one of 

 the vesicles in two. What do you find inside it? 

 "What is the nature of its wall ? Being careful not 

 to injure the vesicle, cut off a portion of the branch 

 about an inch long, containing one or more vesi- 

 cles, and throw the piece into salt water. Does 

 the piece float or sink ? Try the same experiment 

 with another portion of the branch free from ves- 

 icles. What result ? What is the use of the ves- 

 icles in a plant which grows attached to a solid 

 substratum ? 



Examine the tips of some of the branches. Do 

 you find them swollen and covered with tufted 

 points, the conceptacles ? Do these conceptacles 

 have a definite arrangement ? Do you find them 

 elsewhere than on the tips of the branches ? Do 

 they occur on the midribs ? On both sides of the 

 branch? Pinch such a tip. Is it as firm and 

 hard as the rest of the thallus ? Examine some 

 of the conceptacles with a hand-lens. What is 

 the cause of the tufted appearance? Can you 

 find in the centre of each tuft an opening, the 

 ostiole, which leads into the cavity of the concep- 



