68 FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAMS. 



contact. At length the top of the antheridium opens; the loose cells are discharged 

 into the surrounding water derived from rain or dew, and from each of them is set 

 free a spirally-coiled spermatozoid furnished as regards its anterior half with 

 bristling cilia (see vol. i. p. 29, fig. 7 "). The spermatozoids manifestly direct their 

 course to an amphigonium as they whirl about in the water. Meanwhile the canal- 

 cells of neck of the amphigonium have been partially converted into mucilage; some 

 mucilage is discharged into the environing water, and it seems that concomitantly 

 with this organic acids have been evolved in the region of the amphigonium, which 

 exercise an attractive influence on the spermatozoids. What is known as a fact is 

 that the sf)ermatozoids accumulate in this mucilaginous mass and also penetrate 

 through the slimy substance left behind in the canal of the amphigonial neck. 

 Thus they reach the ooplasm which is hidden in the oogonium at the bottom 

 of the fruit-rudiment. As it has repeatedly been observed that spermatozoids 

 make their way into the ooplasm and there disappear, we may assume that 

 the delicate envelope of the ooplast is pierced by the spermatozoid, and that 

 thereupon a coalescence between the two kinds of protoplasm takes place {cf. also 

 figs. 346i-,3, 4) 



The fertilized ooplasm now subdivides into several cells with partition-walls 

 inserted between them, and thus is produced a multicellular embryo which remains 

 embedded in the unaltered amphigonium. This structure, though scarcely differing 

 at all from the fruit-rudiment, must be considered as a fruit. After a .short period 

 of rest the embryo germinates, and the new generation, which gradually makes its 

 appearance as stem, roots, and fronds emerging from the embryo, continues for a 

 short time to receive its food-stuffs through the mediation of the parental pro- 

 thallium. At length, when the new generation has grown sufliciently strong, and 

 is capable of taking up food-stuffs directly from the surrounding air and soil, and 

 of transforming them into constructive materials, the assistance of the prothallium 

 becomes superfluous. The prothallium then withers, and by the time the sporo- 

 genous fronds have developed it has vanished, and no trace of it remains. 



The Horse-tails (Equisetaceas) have, in the main, the same features as the Ferns 

 just 'described as typical of the Vascular Cryptogams in all that relates to the forms 

 of prothallium, antheridia, and fruit-rudiments. The prothallium produced from 

 the spore is at first delicate and ribbon-shaped, but later becomes multifariously 

 lobed, and in form recalls the thallus of certain Liverworts, or sometimes even 

 resembles a little curled foliage-leaf. In most species antheridia and fruit- 

 rudiments grow on different prothallia. Where this is not the case, fertilization 

 of the ooplasm by spermatoplasm arising from the same individual is rendered 

 impossible by means of a disparity between the organs concerned in respect of 

 the time at which they mature. The prothallia which give rise to antheridia 

 are always much smaller than those which produce the fruit-rudiments. The 

 antheridia develop from superficial cells at the end or on the margin of the lobate 

 prothallium, whilst the fruit-rudiments, on the other hand, are derived from super- 

 ficial cells in the recesses between the lobes (see fig. 190^). The spermatozoids 



