/ll 



CRYTOGAMOUS TYPES. 



bodies, having a gei-m-cell — the oosphere — in the lower 

 enil. Tlie antherozoids, on escaping from the anthcridia. 

 make their way down the necks of the arcliegonia, and 

 coming in contact with the oospheres fertilize them. As 

 a result of this fertilization, a plant is developed in all 

 respects like the one which originally bore the spoi-es on 

 its fronds. 



It is manifest, then, that we have here two distinct yenera- 

 tions : first, the spore produces the prothallium which 

 bears the antheridia and archegonia ; secondly, the in- 

 teraction of these gives rise to a plant which bears the 

 spores. This phenomenon is spoken of as the alternation 

 of generations. 



The stems and roots of Fei'ns are found to contain vascular 

 bundles which, like those of monocotyledons, are closed. 



For a description of our common Ferns differing in detail 

 from the Polj'pody, the student is referred to the Flora, 

 page 1G9. 



Horsetails. 



Fig. 298 is a view of the fertile stem of Equisetum arvense, 

 the Common Horsetail, of about the natural size. It 

 may be observed' early in spring almost anywhere in 

 moist sandy or gravelly soil. It is of a pale brown 

 colour and in place of leaves there is at each joint a sheath 

 split into several teeth. At the summit of the stem is a 

 sort of conical catkin, made up of a large number of six- 

 sided bodies, each attached to the stem by a short pedicel. 

 Each of these six-sided bodies turns out on examination 

 to be made up of six or seven sporangia or spore-cases, 

 which ojDen down their inner margins to discharge their 

 spores. Figs. 299 and oOO are enlarged outer and inner 

 views of one of them. The spores themselves are of a 

 similar nature to those of the Ferns, and reproduction is 

 carried on in the same manner ; but each spore of the 

 Horsetail is furnished with four minute tentacles which 

 closely envelope it when moist, and uncoil themselves 

 when dry. 



The fertile stems will have almost withered away by the time 

 the sterile ones appear. These latter are of the same 

 thickness as the fertile ones, but they are very much taller 

 and are green in colour. Observe, also, the grooving of 

 the sterile stem, and the whorls of 4-angled branches pro- 

 duced at the nodes. 



The six)res, upon germination, give rise to prothallia bearing 

 antheridia and archegonia precisely as in the Ferns. The 

 prothallium is usually small, flat, and irregularly branched 

 or lobed, developing the antheridia at the projecting ends 

 of the lobes, and the archegonia in the angles between 



Fig. 298. 



Fig. 300. 



Fig. -I'M. 



