INTRODUCTION TO CRYPTOGAMIC BOTANY. 659 



difference of the stems. Indeed, Lycopods, though attaining 

 so great perfection, and on the whole presenting the highest 

 cryptogamic types, are, as regards the tissues, scarcely so near 

 to Phaenogams as Equisetacece and MarsileacecB, though the 

 former present a lower type of fruit, notwithstanding the great 

 development of the stems in the fossil genera, while the latter, 

 with a form of fruit and tissues of equal if not superior dignity, 

 bear the same relation as regards the stem to the higher Lyco- 

 pods, that degraded aquatic Phcenogams do to more highly 

 organized terrestrial plants of the same natural order. Isoetes, 

 indeed, with a degraded habit, has tissues as highly organized 

 as those of Equisetum or MarsileacecB. 



639. Isoetes has a globose rhizoma sending down many 

 strong roots from the base and deeply umbilicate above, in 

 such wise that the base of the youngest frond is lower than 

 that of the older. The fruit is incorporated with the base of 

 the leaf, but, morphologically speaking, is axillary, like the 

 sporangia of Lycopodium. Above the fruit is a small 

 appendage resembling the ligule of a grass. The sporangium 

 when divided exhibits a number of threads, to which the 

 spores are attached. The latter are globoso-tetrahedric and 

 naked, like those of Lycopodium. The fruit, therefore, bears 

 a manifest relation both to that of Marsileacece and Lycopo- 

 diacew ; the former it resembles in the approach to a multil- 

 ocular receptacle, like that of Marsilea; the latter in the 

 axillary mode of growth and the naked globoso-tetrahedric 

 spores. The leaves possess stomates, and there are annular 

 vessels in the roots and rhizoma, in which it resembles Equi- 

 setum. The spermatozoids are, according to Hofmeister,* like 

 those of Equiseta and Ferns. The germination is like that of 

 Lycopodium. On the whole, therefore, notwithstanding the 

 difference in tissue, it should seem that it is a true Lycopod. 

 Isoetes occurs in many parts of Europe, the north of Africa 

 and America, Brazil, Australia, Hindostan, &c. There are 

 several well-characterised species, some of which are beauti- 

 fully illustrated in the Flora of Algeria. AU the species are 



* Beitrage zur Kenntniss der Gef asscryptogamen. W. Hofmeister, 

 Leipzig, 1852. 



