FILIOIN^. 369 



placing fresh spores In water, or upon moist earth or moist pieces of 

 porous pottery. It must, however, be borne in mind that vpithin a few 

 days after reaching maturity the spores lose their power of germinating. 

 (d) The oldest genus of this order is Equisetites, represented in the 

 Carboniferous by several species. Equisetum extends from the lower 

 Secondary (Triassic) to the present. 



§ II. Class Filici]<c^. 



483. — The plant-body of the asexual generation in this 

 class consists of a solid stem, bearing roots and broadly ex- 

 panded leaves, the latter usually on long petioles. Tlie 

 stems are mostly horizontal and underground, but in some 

 cases they rise to a considerable height vertically in the 

 air. The leaves arise singly upon the stems, and grow up- 

 ward from the rhizome (horizontal stem), or are borne as a 

 crown upon the more or less elongated upright stem. The 

 leaves, are in nearly all cases supplied with fibro- vascular 

 bundles, which run as veins through the parenchyma ; there 

 is usually a prominent midrib, upon each side of which the 

 parenchyma is permeated with small veins, which are free 

 (running more or less parallel from the midrib to the margin), 

 or reticulated. 



484. — The Filicinse are for the most part terrestrial plants 

 of considerable size, a few only being small or of ' an aquatic 

 habit. They are all richly supplied with chlorophyll, and 

 none are in any degree parasitic. Nearly all the species are 

 perennial, in some cases, however, dying down to the 

 ground at the end of the summer, the underground portions 

 alone surviving the winter. 



485. — The prothallium in "the Filicinse is a small cell- 

 ular body,* composed in most cases of chlorophyll -bear- 

 ing parenchyma. It is frequently somewhat heart-shaped. 



* Dr. Farlow, in a paper on " An Asexual Growth from the Pro- 

 thallus of Pteris cretica," in Proc. Am. Acad. Arts and Sciences, 1874, 

 and Qr. Jour. Mic. Science, 1874, described certain prothallia in which 

 gcalariform vessels were found by him. These abnormal prothallia 

 produced new plants directly, without the intervention of the usual 

 process of fertilization ; the scalariform vessels of the prothallia were 

 in every case continuous with those in the new plants. 



