90 A LABORATORY MANUAL OF BOTANY 
epidermal outgrowth (the indusium), the sporan- 
gia, and the spores. Allow some sporangia to dry 
under a low power and determine how they distrib- 
ute their spores. 
General questions.— Which generation of a fern does the 
greater amount of nutritive work? What are its structural 
advantages for this work? In what way does this sporo- 
phyte differ from that of a moss plant? Compare the moss, 
the liverwort, and the fern with reference to their gameto- 
phyte structures; also with reference to their devices for 
asexual spore distribution. 
LESSON LIV 
General exercise on Pteridophytes' 
Specimens of the horsetail or scouring-rush (Hquise- 
tum), of the ground-pine or club-moss (Lycopodium or Se- 
laginella), and ordinary ferns showing varying habits, 
should be studied as to their general characters, both as to 
the general structure and habit of the plant body and the 
methods of asexual reproduction. Make sketches of forms 
studied. 
The gametophyte stage becomes so obscure in the higher 
forms that the casual observer never sees it. It finally be- 
comes devoid of chlorophyll, and so small that it is seen 
only by means of magnification. But it continues to retain 
its ability to develop the gametes, which form the sex spore, 
and this of course proves if to be a gametophyte. 
A further complication that arises in some of the highest 
ferns, and one that is difficult to understand, is found in 
the fact that the asexual spores are unlike, one being very 
large and one very small. These dissimilar asexual spores 
produce unlike gametophytes. The small gametophyte, 
developed from the small spore, produces the male gamete, 
1 Tf there is abundant time, this work should occupy two lessons, 
