SEXUAL GENEEATION OF FERNS 679 



and this again undergoing horizontal subdivision, the lower half be- 

 comes the oosphere or germ-cell, whilst the upper extends itself into 

 the neck. By the conversion into mucilage of a central row, an open 

 passage or canal is formed, through which the antherozoids make 

 their way to the oosphere lying at its bottom (fig. 522, B, a). The 

 oosphere, when fertilised 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 Ophioglossacece 

 (adder's-tongue ferns), the development of the prothallium takes 

 place underground* in the form clt-a small roundish tuber, composed 

 of parenchymatous tissue containing no chlorophyll, and producing 

 antherids and archegones on its upper surface. 



The early development of the embryo-cell takes place according 

 to the usual method of repeated 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 archegone, which organ in the 

 meantime is becoming atrophied. In the very beginning of its 

 development the tendency is seen in the cells of one extremity to 

 grow upward so as to evolve the stem and leaves, and in those of the 

 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, the prothallium decays 

 away. Thus, then, the * spore ' of the fern must be considered as a 

 generative 'gonid ' 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 pur- 

 pose of ' nursing ' the embryos originated by the generative act ; 

 which embryos finally develop themselves, not, as in mosses, into 

 mere sporogones, but, as in Phanerogams, into entire plants, com- 



1 The study of the development of the spores of ferns, and of the act of fertilisa- 

 tion 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 ensured, 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 antherids, and bear abundance of 

 archegones, those which have remained behind in their growth are beginning to be 

 covered with antherids. If the crop be now kept with little moisture for several 

 weeks, and then suddenly watered, a large number of antherids and archegones 

 simultaneously open ; and in a few hours afterwards the surface of the larger pro- 

 thallia will be found almost covered with moving antherozoids. Such prothallia as 

 exhibit freshly opened archegones 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 its surface. Of these sections, which, after much 

 practice, may be made no more than one- fifteenth of a line in thickness, some will 

 probably lay open the canals of the archegones ; and within these, when examined 

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

 tinguished. The prothallium of the common Osmunda regalis will be found to 

 afford peculiar facilities for observation of the development of the antherids, which 

 are produced at its margin. 



