and Laboratory Methods. 2613 



LXI. Ferns. General study. 



(a) Adiantnm capilhis 7'eiieris L. Venus-hair Fern. 



Class, Filices. Order, Filicales. Family, Polypodiaceae. 



The Venus-hair fern grows in ravines and is widely distributed, but very 

 rare in the North. It grows very readily in greenhouses, and is extensively 

 cultivated. The gametophytes may be found at almost any time on pots in 

 greenhouses. They may be raised in large quantities by sowing spores on any 

 well-prepared, moist ground. 



Gametophyle. 



1. Mount a fresh, heart-shaped thallus in water and sketch it from the upper 

 side under dissecting microscope. 



2. Study the rhizoids under low power and draw a single one under high 

 power. Are they unicellular or multicellular? 



3. Under high power draw a single cell of the thallus, showing the chloro- 

 plasts. 



4. Examine the lower side carefully under low power and note the numer- 

 ous antheridia and archegonia. How are these organs distributed over the 

 thallus? Under high power draw an antheridium and an archegonium (so much 

 as can be seen of them above the surface of thallus). Compare the thallus of 

 Adiantum with Anthoceros and Marchantia. Note especially the small compar- 

 ative size. 



5. Look for the large, spirally coiled spermatozoids moving in a ripe anther- 

 idium. Study free-swimming spermatozoids and draw. Describe the movement. 

 The spermatozoids can usually be found on gametophytes of proper size and 

 are often present in large numbers. lodin will bring out the flagella. 



6. If prepared slides are available, draw section of nearly mature anther- 

 idium, showing spermatozoids in various stages of development; also draw an 

 archegonium, showing the neck, venter and oosphere. 



Sporophyte. 



7. Sketch and describe the compound leaf. 



8. Mount and draw a single leaflet under dissecting microscope, showing 

 the general outline and the free, dichotomous venation. How does the charac- 

 ter of the venation explain the notched and cut margin? Can the origin of the 

 leaflets be explained from the same standpoint ? Note that the tips of some of 

 the lobes are bent under so as to cover the sporangia. 



9. Under high power study and draw the stomata. Are they on the upper 

 or lower surface or on both? Draw a single cell, showing the chloroplasts. 



10. If slides are at hand draw a section of a young sporophyte embryo, 

 showing four definite regions (quadrants). 



11. Pick out a young sporophyte from the underside of an old gameto- 

 phyte, and draw under low power. Show the four regions, first leaf, root, bud 

 and foot. Note that the young sporophyte is parasitic on the parent gameto- 

 phyte, and that it acquires its independent life gradually. 



