i SELAGINELLACEM . , 47 



privileged cell are formed four spores, the number usually present in 

 the mature megasporange. The microspores are formed in the same 

 way as in the other heterosporous families. After falling out of the 

 sporange they frequently adhere together in fours. The microspore 

 has three coats — endospore, exospore, and epispore — of which the inner- 

 most is composed of cellulose. The coat of the megaspore is also 

 treble, and the epispore is not unfrequently beautifully granulated and 

 spiny. The dehiscence of both kinds of sporange is caused by the 

 unequal contraction of the epidermal cells. The microsporanges are 

 2-valved, the megasporanges 3-4-valved. 



The genus Selaginella (Spring) includes above 300 species, spread 

 over the whole globe, but most abundant in the tropics. Many species 

 resemble Lycopodium very closely in habit, but are more moss-like, 

 and the leaves generally more delicate ; in others the stem is erect, and 

 they reach the magnitude of small shrubs. Several species are favourite 

 objects of cultivation from the beautiful metallic lustre of the leaves. 

 They are readily propagated non-sexually, a small fragment of the stem 

 producing a new plant if kept warm and moist on loose earth, owing to 

 the production of adventitious roots in the angle formed by the branch- 

 ing of the ' vascular ' bundle of the leaf from that of the stem. No 

 economical use is known of any species either of Selaginella or 

 Isoetes. 



Order 2. — IsoetEvE. 



In the single genus Isoetes the general phenomena of the life-history 

 correspond to those of Selaginella, but with some important differences. 

 Some weeks after the escape of the megaspore from the decaying mega- 

 sporange its cavity becomes filled, by free-cell-formation, with a number 

 of naked primordial cells, which gradually fill up the whole cavity of the 

 endospore, and then become converted into a cellular tissue by the in- 

 vestment of each with a cell-wall of its own. The endospore at the 

 same time thickens, and separates into several layers with a finely granu- 

 lar structure. The epispore, or outer layer of the coat of the megaspore, 

 now splits at its apex by a three-rayed fissure, exposing the endospore, 

 which also subsequently disappears, and a portion of the spherical pro- 

 thallium is thus laid open. At its exposed apex appears the first arche- 

 gone, which is followed by others if the first is not fertilised. The 

 archegones resemble those of Selaginella, except that each of the rows 

 which constitute the neck is composed of four instead of two cells. 



The microspores are yellowish grey, and of the form of the quadrant 

 of a sphere. The antherozoids are very long, slender, and attenuated 



