4 ENGLISH BOTANY. 



leaves bearing macrosporangia and those bearing microsporangia. 

 Macrospores large, with a whitish crustaceous integument, sub- 

 globular, trigonous towards the apex, the division between the hemi- 

 spherical and the trigonous portion, and those between the three faces 

 of the trigonous part marked by elevated lines, the trigonous portion 

 ultimately opening into three valves. Microspores very numerous 

 and very minute, grey, oblong-trigonous, marked by a single line. 

 Macrospore developing a prothallium at its apex, which has its 

 oosphere fertilised by the antherozoids developed in the microspores, 

 as in the Marsiliaceaa. 



GENUS I.— I S O E T E S. Linn. 



The only genus. Characters the same as those of the Order. 



Name from To-os (isos), equal, and Itos (etos), year, from the plant having the same 

 appearance all the year round. 



SPECIES I.-I S O E T E S LACUSTRIS. Linn. 

 Plates 1826 and 1827. 



Plant aquatic, submerged. Roots glabrous. Conn 2-lobed, not 

 clothed with the persistent and hardened bases of former leaves. Leaves 

 subcylindrical or tetragonous, subulate, with broad sheathing bases 

 having membranous edges and smooth backs, straight or recurved, 

 erect or ascending, more or less translucent, without marginal bast- 

 fibres, and without stomata or with very few. Phyllodes absent. 

 Yelum incomplete. Sporangia oblong-ovoid oval-ovoid or subglobose, 

 unspotted. Macrospores with a white crustaceous integument, tuber- 

 culate, with the tubercles not coalescing into ridges. Microspores 

 smooth. 



Subspecies I.— Isoetes eu-lacustris. 



Plate 1826. 



Babenh. Crypt. Vase. Europ. Nos. 5 and 77. 



I. lacustris, Durieu et Auct. plur. Bab. Man. Brit. Bot. ed. vii. p. 456. Milde, 

 Filices Europ. p. 276. 



Plant aquatic, submerged. Root-fibres glabrous. Corm '2-lobed, with 

 3 to 7 longitudinal furrows, not clothed with the persistent and hardened 

 bases of former leaves. Leaves slightly translucent, dark green, sub- 

 cylindrical-terete or subulate, with broad sheathing bases having 



