314 THE BIOLOGY OF THE PLANT 



is their shape? Of what kind of tissue are 

 they composed? Are they of the same thick- 

 ness throughout ? Do the cells have the same 

 contents as those of the thallus ? Examine the 

 margin of a single gemma and find the scar at 

 the point where the gemma was attached to its 

 pedicel or stalk. What is the shape of the 

 scar ? What is the arrangement of the neighbor- 

 ing cells ? Find also two vegetative notches. 

 How are they situated in reference to each 

 other and to the scar? How do you distin- 

 guish them from the scar? What is the posi- 

 tion of the margins of the gemma on each side 

 of the notch ? Examine the base of the notch 

 in large, mature gemmae for small papillae, 

 which are the early stages of the young plants 

 to which the gemmse give rise. Why should 

 these organs be called "gemmae"? Having 

 examined one surface of a gemma, turn it over 

 and examine the other side. Are the two sides 

 unlike ? In what ways may gemmae be distrib- 

 uted? What position would they naturally 

 assume upon the ground? Is their structure 

 at all related to the manner in which they pro- 

 duce new thalli ? 



Draw several gemmae of various sizes. Cut 

 off a cupule and mount it in a drop of water. 

 Examine it with a low power. Notice again 

 the shape of its margin. Put on a high power 

 and study the structure of the cupule, noting 

 the gemmae on the inside, and its toothed mar- 

 gin. Draw. Examine a young cupule. How 

 does it differ in structure from the mature or- 

 gan ? Draw. Make transverse sections through 



