282 THE BIOLOGY OF THE PLAUT 



the leaves ? At all of the nodes ? Are all the rhi- 

 zoids surrounded by masses of mud? Examine 

 under the low power. What is the arrangement 

 of the rhizoids borne at one point on the stem ? 

 Are they arranged in whorls? Do they origi- 

 nate from particular cells? If so, from which 

 cells? Do two or more rhizoids originate from 

 the same cell ? Put on the high power and study 

 a single rhizoid. What is its shape ? Does it vary 

 in diameter ? Is it segmented ? Does it have a 

 layer of cortical cells ? Of how many cells does 

 it consist ? What are its contents ? Note the cir- 

 culation of the protoplasm, which will be studied 

 later. 

 Draw several rhizoids, showing their shape, structure, 



mode of attachment to the stem, contents, etc. 



If specimens of Nitella can be obtained they should 



be compared with Chara. 



PHYSIOLOGY 



a. Growth. — Put a single vigorous plant into a dish of 

 water. With a pair of dividers accurately meas- 

 ure each internode, beginning at the lower end of 

 the plant, and record the measurements. What 

 is the length of each internode and of the entire 

 plant? Place the dish in a window where the 

 plant may have plenty of sunlight. At the end of 

 a week measure all of the internodes again and 

 record the measurements. Do this for two or 

 three weeks in succession. How much has the 

 plant grown in length in this time? Is the in- 

 crease due to the formation of new internodes or 

 to the lengthening of those already formed at the 

 beginning of the experiment or to both ? If to 



