Fig. 5
Fig. 6
A frond that is only once-pinnate may seem at first glance twice-pinnate, as its pinnæ may be so deeply lobed or pinnatifid as to require a close examination to convince us that the lobes come short of the midvein of the pinnæ. In a popular hand-book it is not thought necessary to explain further modifications.
The veins of a fern are free when, branching from the midvein, they do not unite with other veins ([Fig. 5]).
Ferns produce spores ([Fig. 6]) instead of seeds. These spores are collected in spore-cases or sporangia ([Fig. 7]). Usually the sporangia are clustered in dots or lines on the back of a frond or along its margins. These patches of sporangia are called sori or fruit-dots. They take various shapes in the different species. They may be round or linear or oblong or kidney-shaped or curved. At times they are naked, but more frequently they are covered by a minute outgrowth of the frond or by its reflexed margin. This covering is called the indusium. In systematic botanies the indusia play an important part in determining genera. But as often they are so minute as to be almost invisible to the naked eye, and, as frequently they wither away early in the season, I place little dependence upon them as a means of popular identification.
A fertile frond is one which bears spores.
A sterile frond is one without spores.