LIFE HISTORY OF A FERN 159 
spores may be formed; a sorus will consist of fully 100 sporangia, usually 
more; 20 is a moderate estimate of the son on an average pinna; there may 
be fully 50 fertile pinnae on one well-developed leaf, and a strong plant 
would bear 10 fertile leaves. 48 X 100 X 20 X 50 X 10 = 48,000,000. 
The output of spores on a strong plant in the single season will thus, on a 
moderate estimate, approach the enormous number of fifty millions." 
148. Types of Sporophylls* In many ferns the leaves 
serve both vegetative and reproductive functions in about 
FIG. 119. The cinnamon fern (Osmunda cinnamomea) , showing foliage 
leaves and sporophylls. 
equal degree, as in the case of Poly podium mentioned 
above. In some species, however, there are two kinds of 
leaves one devoted entirely to vegetative functions, and 
another to the reproductive, or spore-producing function 
(Fig. 119) ; between these two extremes all grades of trans- 
ition are found (Fig. 120). But however widely the sporo- 
