1918] STOKEY—APOGAMY 99 
moist peat. They were, however, exposed to rather intense light. 
It seems to be true that one explanation will not answer for all 
cases; the factors which cause apogamy in Woodsia ilvensis, a 
Fics. 1-3, 5.—Dicksonia squarrosa: fig. 1, prothallium with two apogamous buds, 
X22; fig. 2, section through a, X 210; fig. 3, section through b, X210; fig. 5, section 
of prothallium with archegonia and archegonial projections, X90. Fig. 4, Cyathea 
Tussacii: archegonial projection, 170. 
species which grows in exposed situations, are not necessarily the 
Same as those which cause it in the species which grow in shaded 
places. 
