92 MORPHOLOGY AND LIFE HISTORY 



D. Microscopic Characters: 



1. The rhizoids. 



(a) With the forceps carefully remove a few of the 

 rhizoids and mount them in clearing fluid. 

 Examine them first under low, then under high 

 power. 



(b) Do you find different kinds of rhizoids? If so, 

 how are they distinguished? Are there cross- 

 walls? Describe the contents of the rhizoids. 

 Do they branch? Explain the shape of their 

 tips, and the thickness of their cell-walls. 



2. The gemmae. 



(a) Remove several gemmae with a scalpel, being 

 careful not to cut or otherwise injure them, 

 and mount them in a drop of water. Examine 

 with low power. 



(b) Are the gemmae more than one cell thick? Is 

 their thickness uniform? Describe. 



(c) Find on the margin the scar, where the gemma 

 was attached to its pedicel, or stalk. 



(d) Find two vegetative notches, 180 apart. How 

 do they differ from the scar? Find papilla-like 

 cells in these notches. Do they contain chloro- 

 phyll? Do they secrete mucilage? In the 

 apex of each of these notches is a vegetative 

 point from which a new thallus will develop. 

 The mucilage protects it. 



(e) Are there any surface outgrowths? Is there 

 dorso-ventral differentiation? Compare them 

 in this respect with the thallus to which they 

 give rise. So far as you can detect, would it 

 make any difference which side up the gemma 

 lay when it was sown? 



