454 



BOTANY 



PART II 



prothallium is filiform and branched, resembling in structure the protonema of 

 the Mosses, and producing the antheridia and archegonia on lateral branches 

 (Fig. 399). 



The ANTHERIDIA and archegonia ('■*) are similarly constructed in nearly all 

 Leptosporangiatae, and present differences from those of the Eusporangiate Ferns ; 

 those oi Folijpodium vulgare (Figs. 400, 401) may serve as a type. The antheridia 

 are spherical projecting bodies (Fig. 400, A, p), arising on young prothallia by the 

 septation and further division of papilla-like protrusions from single superficial 

 cells. When mature, each antheridium consists of a central cellular cavity, filled 

 with spermatozoid mother- cells, and enclosed by a wall formed of two ring-shaped 

 cells {A, 1, 2) and a lid-cell (3). The spermatozoid mother-cells are produced by 

 the division of the central cell. They are discharged from the antheridium by the 

 pressure exerted by the swollen ring cells, and the consequent rupturing of the 

 lid-cell. Each mother-cell thus ejected liberates a spirally coiled spermatozoid. 

 The anterior extremity of the spermatozoid is beset with numerous cilia, while 

 attached to its posterior end is a small vesicle which contains a number of granules, 



Fkj. 401. — Polt/podiiim vulgare. A, Young archegonium not yet open ; A", neck-oanal-cell ; 

 K", ventral-canal-cell ; o, egg-cell ; B, mature archegonium, open, (x 240.) 



and represents the unused remnant of the contents of the mother-cell (Fig. 400, 

 A C; Fig. 99, ^). 



The archegonia arise from the many-layered median portion of older prothallia. 

 They are developed from a single superficial cell, and consist of a venti-al portion, 

 embedded in the prothallium, and a neck portion. The neck, which projects 

 above the surface of the jirothallium, consists of a wall composed of a single layer 

 of cells made up of four cell rows (Fig. 401, A, B) ; it encloses the elongated neck- 

 canal-cell. The ventral portion contains the large egg-cell and the ventral-canal- 

 cell immediately above it. As the archegonium matures, the canal-cells become 

 disorganised, and fill the canal with a strongly refractive mucilaginous substance. 

 This swells on the admission of water, and, rupturing the neck at the apex, is 

 discharged from the archegonium, which is now ready for fertilisation. The 

 development of the embr3'o is represented in Fig. 389. 



In certain ferns the sporophyte may originate on the prothallus by a process of 

 budding or direct vegetative growth ; the sexual organs are not formed or take 

 no part in the production of the plant (apogamy). Conversely the prothallus may 

 arise directly, without the intervention of spores, from the tissues of the leaf 

 (apospory) ('•*"). 



Okku'Iai,. — Anjiidivm friix man, Fii.ix mas. 



