EXERCISE 124 



In the highest plants the gametophyte is always parasitic on the sporophyte, whereas in the lower 

 plants (mosses) the sporophyte is parasitic on the gametophyte. 



Problem. Are there any plants in which the two generations are about equally self-sustaining ? 



What to use. Fern plants, complete, with fruiting dots ; prothalli of fern ; magnifying glass ; micro- 

 scope with slides etc. 



What to do. 1. Examine the fern plant and note structure of underground stem, roots, leaf, and 

 spore areas on underside or at edge of frond. Examine spore cases and spores under microscope, noting 

 especially the part of the spore case that is related to the scattering of the spores. 



NOTE r. The familiar stage of the fern plant is the sporophyte. It develops from a fertilized egg and bears spores. 



2. Examine prothalli under the microscope as well as with magnifying glass. Study under surface as 

 well as upper. Note rhizoids, like root hairs ; archegonia near the front edge and antheridia near the 

 hind edge. 



NOTE 2. The prothallus is the gametophyte ; it develops from a spore. Eggs and sperms are borne on one individual. 

 After fertilization the egg develops into a sporophyte. 



Record. Make drawings and label to show the following stages and structures : 



1. The sporophyte as a whole, with characteristic leaves, rootstock (underground stem), and absorbing 

 organs. 



2. The fruiting dots, or masses of spore cases : microscopic view of (a) spore case entire ; (b] spore 

 case broken ; (c) spores. 



3. The gametophyte (upper surface), enlarged. 



4. Lower surface of gametophyte, under microscope : (a) rhizoids ; (&) archegonia ; (c) antheridia ; 

 and, if possible, (d) egg and sperm cells. 



[134] 



