154 



BOTANY 



ar_. 



-vh 



Home Experiment. — Plant some spores on the surface of a moist brick 

 or broken flowerpot. Cover them with a piece of glass so as to keep the 

 air in which they remain warm and moist. Give them moderate heat 

 (about 70° Fahrenheit) . After two or three weeks, if the surface is care- 

 fully scanned with a hand lens, very tiny green threadlike structures may 

 be found. These structures grow rapidly to form flat heart-shaped bodies. 



Prothallus. — Such a structure is called a prothallus. The pro- 

 thallus clings to the surface of the brick by means of tiny rootlike 



organs called rhizoids. The 

 whole structure is another 

 stage in the life of the fern 

 plant. A careful examination 

 of the prothallus with a com- 

 pound microscope reveals the 

 fact that scattered among the 

 rhizoids are some tiny rounded 

 elevations ; immediately above 

 the rhizoids and between them 

 and the little groove in the 

 prothallus are other struc- 

 tures ; both the above structures 

 are too minute to find with 

 the naked eye. 



Archegonia. — The last-named are called archegonia; they are 

 found to be very tiny flask-shaped organs almost embedded in the 

 surface of the prothallus. Each archegonium contains a single 

 large cell. This we recognize as an egg cell. 



Antheridia. — The other structures found among the rhizoids are 

 called antheridia. Each antheridium contains a large number of 

 very minute objects which are able to move about in water by 

 means of lashlike threads of protoplasm. Each of these motile 

 cells is called an antherozoid; they have, in fact, the same function 

 as the sperm cells of the flowering plants. Because this part of 

 the plant holds the egg cells and sperm cells, it is called the sexual 

 generation of the fern. 



Fertilization. — The sperm cells swim to the egg cells in water 

 (rain or dew), being attracted to the mouth of the flask-shaped 

 archegonium by an acid secretion which is poured out by the cells 



Prothalium of a common fern (Aspidium); 

 A, under surface, showing rhizoids, rh, 

 antheridia. an, and archegonia, ar; B, under 

 surface of an older gametophyte, showing 

 rhizoids, rh, and young sporophyte, with 

 root, w, and leaf, h. (From Coulter, Plant 

 Structures.) 



