CRYPTOGAMS 253 



(rhizoids)? If so, where are they found ? If your magnifier 

 is very strong, you may be able to find minute protuberances 

 on the under side. They are the sex organs of the fern plant. 



After a few days longer, observe the prothallia again, and 

 you will doubtless find tiny fern plants growing from them. 



Where do these come from? Is there any advantage in 

 the shape of a prothallium? If so, what ? 



Ferns like mosses show the phenomena of alternate gen- 

 erations. The sporophyte stage is the familiar fern plant. 

 The gametophyte stage is seen in the prothallium with its 

 archegonia and antheridia. 



Note to Teachers. In propagating ferns from spores, water 

 the soil well to begin with, before the spores are sowed. Keep it 

 covered with a plate of glass to prevent drying out. Do not water 

 the culture again until it is desired to have fertilization take place. 

 Prothallia will live indefinitely, and no fertilization occurs if there 

 is no water in which the sperms can swim. After watering, the 

 embryo fern plants will soon appear. 



214. YEAST AND FERMENTATION 

 Object. To study the growth of yeast. 



Method. Prepare two wide-mouth bottles. Fill each 

 one about half full of water in which a small quantity of 

 sugar has been dissolved. 



Add to one bottle a small piece of yeast cake dissolved 

 in water or a teaspoonful of liquid yeast. Let the other 

 bottle remain as a control. Place both preparations in a 

 warm place and allow them to stand for several hours. 



What change, if any, takes place in each bottle? How 

 do the contents of the first bottle differ from that of the 

 second? To what must this difference be due? Note the 

 smell, if any. Plunge a lighted stick into each jar and test 



