DIV. I 



PTERIDOPHYTA 



505 



thickly beset on the inner side with large, nearly spherical sporangia. The course 

 of the vascular bundles and occasional reversions indicate that the fertile segment 

 is derived from the union of two basal pinnae. 



Our knowledge of the peculiar monoecious prothalli of the Ophioglossaceae is 

 largely due to BRUCHMANN ; they are long-lived, subterranean, saprophytic, 

 tuberous bodies without chlorophyll but inhabited by a mycorrhizal fungus. In 

 Ophioglossum (Fig. 467 F) they are cylindrical and radially symmetrical, simple 

 or branched ; in Botrychium (Fig. 467 B, C] they are oval or heart-shaped and 

 dorsi ventral. The antheridia (Fig. 468) and archegonia (Fig. 469) are sunk in 

 the tissue of the prothallus. The antheridium encloses a large spherical mass of 

 spermatozoid mother-cells which are set free when mature by the swelling of the 



FIG. 468. Ophioglossum i-ulgatum. A-C, Stages 

 in the development of the antheridium from 

 a superficial cell ; the upper cell in C gives 

 rise to the cover-cells, the lower to the 

 mother cells of the spermatozoids. D, 

 Antheridium not yet opened ; d, cover-cells. 

 E, Spermatozoid. (After BRUCHMANN.) 



Fie. 469. Ophioglossum vulgatum. A C, De- 

 velopment of archegonium. D, Mature opened 

 archegonium with two spermatozoids ($) in 

 front of the opening ; h, neck-cells ; hk, neck- 

 canal-cells ; o, egg-cell ; b, basal cell. (After 

 BRUCHMANN.) 



contents and the breaking down of one of the central cells of the outer wall. The 

 spermatozoids have a spirally wound body and numerous cilia ; a small vesicle is 

 adherent to the spermatozoid (Fig. 468 E}. The antheridia originate from single 

 superficial cells (Fig. 468 A-C), as do also the archegonia (Fig. 469 A-C). The 

 slightly projecting neck of the latter opens after the neck canal-cell has swollen 

 and disintegrated ; the oosphere (o) remains in the sunken venter. In many species 

 the embryo leads a subterranean existence for several years. The primary root is 

 first formed and soon projects from the archegonium (Fig. 467 C, F, k) ; later 

 the first leaf and the apical cell of the stem are differentiated. In some species of 

 Botrychium the embryo forms an elongated multicellular suspensor at the end of 

 which the proper embryonic mass is formed. In this an agreement with the 

 Lycopodinae is evident (cf. Fig. 493 and Fig. 498), which do not in other respects 

 show any close relationship to the Eusporangiatae. 



Sub-Class II. Leptosporangiatae 

 Order 1. Filiees 



The Filiees, or Ferns, in the narrower sense of the word, comprise 

 a large number of genera with numerous species, being widely distri- 



