336 PRACTICAL COURSE IN BOTANY 



Observe a tiny dot near the center of the rhomboidal areas 

 into which the epidermis is divided and compare it with 

 your drawings of stomata (181, 183). 

 What would you judge that these dots 

 are for? While differing in structure 

 from the stomata of leaves, they serve 



Fig. 477. — ^ A portion ,, , , , , 



of the upper epidermis the Same purposes and may be regarded 

 of marchantia, magni- ^s a morc rudimentary form of the same 



fied, showing rhomboidal 



plates with a stoma in Organ. 



^^*'^- 386. Rhizoids. — Wash the du-t from 



the under side of a thallus and examine with a lens ; how 

 does it differ from the upper surface ? Do you see anything 

 like roots ? Place one in a drop of water under the micro- 

 scope. Compare with similar organs found on the lichen 

 (379). What are they? Would rhizoids be of any use on 

 the upper side ? stomata on the under side ? 



387. Gemmae. — Look along the upper surface for little 

 saucer-shaped (in lunularia, crescent-shaped) cupules {g, g, 

 Fig. 476). Notice their shape and position, whether on a 

 midrib or near the margin. Examine the contents with 

 a lens and see if you can tell what they are. These little 

 bodies, called gemmce, are of the nature of buds, by which 

 the plant propagates itself vegetatively somewhat as the 

 onion and the tiger lily do by means of bulblets. Sow some 

 of the gemma) on moist sand, cover them with a tumbler 

 to prevent evaporation, and watch them develop the thalloid 

 structure. 



388. The fruiting receptacles. — Procure, if possible, 

 thalli with upright pedicels bearing flattened enlargements 

 at the top (Figs. 475, 476). These are thallus branches 

 modified into receptacles containing the reproductive organs, 

 which, in marchantia, are dioecious, the two kinds growing 

 on separate thalli. Notice their difference in shape, one 

 kind being slightly lobed or scalloped, the other rayed like 

 the spokes of a wheel. The first kind are known as antherid- 

 ial, or male, receptacles; the second as aichegonial, or female. 



