Algae, Fungi, and Lichens. 265 



some of it with the point of a knife, and notice whether 

 it readily breaks up into small particles. Observe the tree 

 on which it was growing. Is the growth always on the 

 north side ? How far up the trunk does it extend ? 



152. Scrape up a small portion of the growth with the 

 point of a knife, taking care not to remove the bark, and 

 mount under a coverglass in a drop of water. Place a 

 clean cloth over the forefinger and move" the coverglass 

 about gently, in order to spread out the preparation in a 

 thin film. If the pressure of the finger is too great, the 

 little plants will be broken. Examine with a high power, 

 and pick out what appears to be a single individual. How 

 do you account for the clusters of individuals which are 

 found ? Does the green color occur in definite chloro- 

 plasts ? Treat the preparation with chloral hydrate-iodine. 

 Does starch appear ? Is there any difference in this respect 

 between material which has been kept in the dark and that 

 which has been exposed to the bright light of the northern 

 sky, but not to the direct rays of the sun ? Can you tell 

 why some trees seem to possess this growth more than 

 others ? 



153. Examine some of the green filamentous plants 

 which occur in ponds, lakes, or small running streams. 

 Do they float freely in the water or are they fastened 

 down in any way ? How do you account for the bubbles 

 of gas which collect about these plants in the sunlight? 

 Is there any difference in this respect between plants 

 which are freely exposed to the sun and those which are 

 deeply shaded ? If so, what is the significance of the 

 difference ? 



154. Pick up some of the material and spread it out in 

 the hand. Can you distinguish the individuals of which it 

 is composed ? Can you distinguish the parts of which the 



