The Fern Lover's 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 clustered 

 in dots or lines on the back or margin of a frond, either on 

 or at the end of a small vein, or in spike-like racemes on 

 separate stalks. Sori (singular soriis, a heap), or fruit 

 dots may be naked as in the polypody, but are usually 

 covered with a thin, delicate membrane, known as the 

 indusium (Greek, a dress, or mantle). The family or 

 genus of a fern is often determined by the shape of its 

 indusium; e. g.. 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 whole 

 or in part by a vertical, ela.stic ring (annulus) reminding 

 one of a small, brown worm closely coiled (Fig. 4). As the 

 spores mature, the ring contracts and bursts with consider- 

 able force, scattering the spores. The spores of the differ- 

 ent genera mature at different times from May to Septem- 

 ber. A good time to collect ferns is just before the fruiting 

 season. (For times of fruiting see individual descriptions 

 or clironological chart on page 220.) 



