348 THE MICROSCOPE AND ITS REVELATIONS. 



built up in layers of four cells each, one upon another, so as to form a 

 kind of chimney or shaft, having a central passage that leads down to & 

 cavity at its base. The lower of the two first-formed cells becomes the 

 6 central cell ' of the archegonium; and this again undergoing horizontal 

 subdivision, the lower half becomes the oosphere or germ-cell, whilst the 

 upper extends itself into the ' neck/ and forms a canal filled with muci- 

 laginous protoplasm, through which the antherozoids make their way to 

 the oosphere lying at its bottom (Fig. 233 B, a). The oosphere, when 

 fertilized by the penetration of the antherozoids, becomes the ( embryo- 

 cell ' of a new plant, the development of which speedily commences. 1 In 

 the aberrant group of OpMoglossece (Adders' tongue ferns), the develop- 

 ment of the prothallium takes place underground, in the form of a small 

 roundish tuber, composed of parenchymatous tissue containing no chlo- 

 rophyll, and producing antheridia and archegonia on its upper surface. 



344. The early development of the Embryo-cell takes place according 

 to the usual method of repeated binary subdivision, producing a homo- 

 geneous globular mass of cells. Soon, however, rudiments of special 

 organs begin to make their appearance; the embryo grows at the expense 

 of the nutriment prepared for it by the prothallium; and it bursts forth 

 from the cavity of the archegonium, which organ in the mean time is 

 becoming atrophied. In the very beginning of its development, the ten- 

 dency is seen in the cells of one extremity to grow upward so as to evolve 

 the stem and leaves, and in those of other extremity to grow downward 

 to form the root; and when these organs have been sufficiently developed 

 to absorb and prepare the nutriment which the young Fern requires, ttie 

 prothallium decays away. Thus, then, the ( spore' of the Fern must 

 be considered as a generative gonidium or detached flower-bud, capable 

 of developing itself into a prothallium that may be likened to a receptacle 

 bearing the sexual apparatus. But this prothallium serves the further 

 purpose of 'nursing' the embryoes originated by the generative act; 

 which embryoes finally develop themselves, not, as in Mosses, into mere 



1 The study of the development of the spores of Ferns, and of the act of ferti- 

 lization 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 collected, and should be spread upon 

 the surface of a smoothed fragment of porous sandstone, 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 begining to be covered with antheridia. If the crop be now kept 

 with little moisture for several weeks, and then suddenly watered, a large num- 

 ber of antheridia and archegonia simultaneously open; and in a few hours after- 

 wards, 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, perpen- 

 dicularly to its surface. Of these sections, which, after much practice, may ba 

 made no more than l-15th of a line in thickness, some will probably lay open the 

 canals of the archegonia; and within these, when examined with a power of 200 

 or 800 diameters, antherozoids may be occasionally distinguished. The prothal- 

 lium of the common Osmunda regalis will be found to afford peculiar facilities 

 .for observation of the development of the antheridia, which are produced at its. 

 margin. (See Rev. F, Howlett in " Intellectual Observer," Vol. vii., p. 32.) 



