GENERATIVE ORGANS OF FERNS. 357 



the "germ-cell;" and, by the softening of the membrane at its 

 apex, they are even enabled to enter its cavity, within which a 

 minute " embryonic vesicle" was previously distinguishable. 

 This embryonic vesicle, when fertilized by the antherozoids which 



FIG. 147. 



G 



Archegonium of Pteris serrulata : A, as seen from above ; a, a, a, cells surrounding the base of the 

 cavity ; b, c, d, successive layers of cells, the highest enclosing a quadrangular orifice : B, side 

 view, showing, A, A, cavity containing the germ-cell ; B, B, walls of the archegonium, made up of the 

 four layers of cells, &, c, d, e, and having an opening on the summit ; c, c, antherozoids within the 

 cavity; #, large extremity; h, thread-like portion; i, small extremity in contact with the germ-cell 

 and dilated. 



move actively round it, becomes the primordial cell of a new 

 plant, the development of which speedily commences. 1 By the 

 usual process of duplicative subdivision a globular homogeneous 

 mass of cells is at first formed; but rudiments of special organs 

 soon begin to make their appearance; the germ grows at the 

 expense of the nutriment prepared for it by the prothallium ; and 

 it soon bursts forth from the cavity of the archegonium, which 

 organ in the meantime is becoming atrophied. In the very be- 

 ginning of its development, the tendency is seen in the cells of 

 one extremity to grow upwards, so as to evolve the stem and 

 leaves, and in those of the other extremity to grow downwards, 



1 See Hofmeister, in " Ann. of Nat. Hist.," 2d Ser. vol. xiv, p. 272. The study of the de- 

 velopment of the spores of Ferns, and of the act of fertilization and of its products, may 

 be conveniently prosecuted as follows: Let a frond of a Fern, whose fructification is 

 mature, be laid upon a piece of fine paper, with its spore-bearing surface downwards; 

 in the course of a day or two, this paper will be found to be covered with a very fine 

 brownish dust, which consists of the discharged spores. This must be carefully col- 

 lected, and should be spread upon the surface of a smoothed fragment of porous sand- 

 stone ; the stone being placed in a saucer, the bottom of which is covered with water, 

 and a glass tumbler being inverted over it, the requisite supply of moisture is insured, 

 and the spores will germinate luxuriantly. Some of the prothallia soon advance beyond 

 the rest; and at the time when the advanced ones have long ceased to produce anthe- 

 ridia, and bear abundance of archegonia, those which have remained behind in their 

 growth are beginning to be covered with antheridia. If the crop be now kept with 

 little moisture for several weeks, and then suddenly watered, a large number of anthe- 

 ridia and archegonia simultaneously open ; and in a few hours afterwards, the surface 

 of the larger prothallia will be found almost covered with moving antherozoids. Such 

 prothallia as exhibit freshly opened archegonia, are now to be held by one lobe between 

 the forefinger and thumb of the left hand, so that the upper surface of the prothallium 

 lies upon the thumb ; and the thinnest possible sections are then to be made, with a thin 

 narrow-bladed knife, perpendicularly to the surface of the prothallium. Of these sec- 

 tions, which, after much practice, may be made no more than 1-1 5th of a line in thick- 

 ness, some will probably lay open the canals of the archegonia ; and within these, when 

 examined with a power of 200 or 300 diameters, antherozoids may be occasionally dis- 

 tinguished. 



