FERNS 191 
answered question. The great interest of the Anthoceros 
forms (§ 99) is due to the fact that their sporophytes are 
green and do chlorophyll work; and this has suggested the 
thought that from such green tissue leaves have been de- 
veloped, and thus a leafy sporophyte has been started. 
109. Sporangia.—Upon the under surface of fern 
leaves dark dots or lines are often seen (Fig. 182). These 
are groups of sporangia, usu- 
ally occurring along the veins 
of. the under surface, but some- 
times in long lines along the 
edge, the margin of the leaf 
rolling in and protecting them, 
as in maidenhair fern and com- 
mon brake (Fig. 183), In ferns 
having the groups of sporangia 
away from the margin, each 
group (sorus) is usually pro- 
tected by a delicate flap (indu- 
stum) growing out from the epi- 
dermis, sometimes forming a ; 
pocket (Fig. 182, A) and some- Fic. 183.—Sporangia of ferns, show- 
5 2 : ing marginal lines of sporangia 
times an umbrella-like or shield- protected by the inrolled margin 
like covering (as in shield ferns) the leaf? A. the common brake; 
z , maidenhair fern. 
(Fig. 182, B). The position and 
the shape of the sorus and the character of the indusium 
furnish useful characters in the classification of ferns. 
Most fern leaves do chlorophyll work and _ produce 
sporangia, two very distinct kinds of work. In some 
ferns, however, some of the leaves are sterile, that is, do 
not produce sporangia, the other leaves doing both kinds 
of work; while in other ferns certain leaves or leaf branches 
are set apart to produce sporangia and do no chlorophyll 
work, and vice versa, the two kinds of work thus being 
divided among the leaves or leaf branches. Such a 
