280 



EMBEYOGENY IN FEENS. 



the antheridia, and have a central canal, a, leading down to a large 

 globular cell, c, imbedded in the substance of the prothallus, and 

 containing the embryo-germ, e. The canal is closed at first, and then 

 opens. The spermatozoids enter the archegonial canal and fertilise 

 the germ-cell. After a time this cell divides and gives rise to the 



Fig. 507. 



Pig. 508. 



Kg. 609. 



Fig. 510. Pig. 511. 



embryonic body, whence the stem of the Pern arises (fig. 511 /). 

 The life of the sporangiferous plant is indefinite, as seen in Tree 

 Ferns, while the prothallus is of very short duration. Thus in 

 Ferns the spores contained in the sporangium form the prothallus 

 without impregnation, while this latter process is necessary for the 

 development of the germ, which gives rise to the leafy sporangiferous 



Fig. 507. Cellular prothallium (exothallluin) of a Pern {Pteris hyngifolia), produced by a 

 spore, s, and giving off a root, t, at one end. It consists of numerous cells, and it giyes 

 origin to antheridia, and pistillidia or archegonia. Pig. 508. Antheridia from the prothal- 

 lixun of the Common Bralce [Pteris aguUvna). a, An unopened antheridium ; 6, antheridium 

 bursting at the apex, and discharging free cellules, each containing a spermatozoid : c, 

 antheridium after the discharge of the cellules. Fig. 509. A spermatozoid with cilia, 

 discharged from a cellule in the antheridium of the Forked Spleenwort [Asplenium s&pteti- 

 trioncde). Fig. 510. Archegonium of the Forked Spleenwort (Aspkmwm sept&ntrumaU) 

 immediately after impregnation. a, Canal leading to the ovule or large cell, u, at the 

 base of the archegonium ; e, nucleated embryonic cell, whence the sporangiferous frond 

 proceeds. Spermatozoids from the antheridium reach the canal of the archegonium, and 

 impregnate the ovule. Fig. 511. Touhg plant of a Fern {Pteri£ paiUacea), showing the 

 commencement of the sporangiferous frond, /, arising from the impregnated ovule in the 

 archegonium ; the prothallium, j>, being still attached. 



