406 



BOTANY 



The archegonia arise from the many-layered median portion of 

 older prothallia. They are developed from a single superficial cell, 

 and consist of a ventral portion, embedded in the prothallium, and a 

 neck portion. The neck, which projects above the surface of the 

 prothallium, consists of a wall composed of a single layer of cells 

 made up of four cell rows (Fig. 339, A, B) ; it encloses a central row 

 of cells, the neck-canal-cells. 



Fia. 339. — JPolypodiwm mlgare. A, Young archegonium not yet open ; K', neck-canal-cell ; 

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



The ventral portion comprises the large egg-cell and 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. By means of an acid excretion 

 (malic acid) diffused in the surrounding water the spermatozoids are 

 attracted to the archegonium, and penetrate to the egg-cell. After 

 fertilisation of the egg by one of the spermatozoids, the egg-cell sur- 

 rounds itself with a cell wall, and without entering upon a condition of 

 rest develops into the embryo of the asexual generation, as already 

 described (p. 398, Fig. 331). 



Officinal. — The only representative of the Ferns is Aspidiwm filix 

 mas (Rhizoma filicis). 



Order 2. Hydropterideae (Water-Ferns) 



The Water-Ferns include only a few genera, which are more or less 

 aquatic in habit, growing either in water or marshy places. The macro- 

 and microsporangia do not develop, like those of the Filices, on the 

 under side of the leaves, but are enclosed in special receptacles at their 

 base, constituting sporangial fructifications or sporocarps. To designate 

 this order Bhizocarpae, as was formerly the custom, is not appropriate, 

 as the sporocarps do not arise on the roots, but always on the leaves. 



