. The fern lover's companion; a guide for the Northeastern States and Canada. The Fern Lovers Companion 25. Fig. -t Sporangia and Fruit Dots Fern spores are formed in little sacs known as spore-cases or sporangia (Fig. 4). Thej are usually clusteredin dots or lines on the back or margin of a frond, either onor at the end of a small vein, or in spike-like racemes onseparate stalks. Sori (singular soriis, a heap), or fruitdots may be naked as in the polypody, but are usuallycovered with a thin, delicate membrane, known as theindusium (Greek, a dress, or mantle). The family orgenus of a fern is o
. The fern lover's companion; a guide for the Northeastern States and Canada. The Fern Lovers Companion 25. Fig. -t Sporangia and Fruit Dots Fern spores are formed in little sacs known as spore-cases or sporangia (Fig. 4). Thej are usually clusteredin dots or lines on the back or margin of a frond, either onor at the end of a small vein, or in spike-like racemes onseparate stalks. Sori (singular soriis, a heap), or fruitdots may be naked as in the polypody, but are usuallycovered with a thin, delicate membrane, known as theindusium (Greek, a dress, or mantle). The family orgenus of a fern is often determined by the shape of itsindusium; e. the indusium of the woodsias is star-shaped; of the Dicksonias, cup-shaped; of the aspleniums,Hnear; of the wood ferns, kidney-shaped, etc. In many ferns the sporangia are surrounded in wholeor in part by a vertical, ring (annulus) remindingone of a small, brown worm closely coiled (Fig. 4). As thespores mature, the ring contracts and bursts with consider-able force, scattering the spores. The spores of the differ-ent genera mature at differe
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