2O2 



THIRD GROUP. VASCULAR CRYPTOGAMS. 



cells of the prothallium, and in the Hymenophyllaceae occur also on the protonemal 

 filaments. The protuberance is usually cut off from the mother-cell by a transverse 

 wall, and swells out into a globular form either at once or after forming a stalk-cell ; 

 in some cases the spennatozoids can be produced without any further change in this 

 globular cell, but usually the cell first undergoes divisions 1 which result in giving the 

 antheridium a wall composed of only one layer of cells with chlorophyll-corpuscles on 

 their inner surface, and a central cell which by further divisions produces the not very 

 numerous mother-cells of the spermatozoids. The discharge of the spermatozoids 

 from the mature antheridium is due to rapid absorption of water by the cells which 

 form the wall; these swell considerably, and by the pressure which they exercise on 

 the contents of the antheridium cause its wall to burst at the apex ; then the 



ft A 



m 



FIG. 150. Antheridium of Adiantum Capillus-Veneris, seen in optical 

 longitudinal section. / immature state. // the- spermatozoids already de- 

 veloped. /// antheridium burst, the parietal cells being greatly swollen in 

 the radial direction and most of the spermatozrids escaped ; / prothallium, a 

 antheridium, j- spermatozoid, * its vesicle containing grains of starch. Magn. 

 550 times. 



FIG. 151. Young archegonia of Pteris 

 serrulate after Strasburger; e the oosphere, 

 h h the neck, k the neck-canal-cell. Further 

 explanation in the text. 



spermatocysts issue forth, and each liberates a spermatozoid which is coiled three 

 or four times in a cork-screw spiral ; its finer anterior extremity is beset with 

 numerous cilia, the thicker posterior end often drags after it a vesicle containing 



1 These divisions take place in a very remarkable manner ; in Ancimia hirta an arched wall 

 arises in the hemispherical projecting mother-cell of the antheridium, and divides it into an inner 

 hemispherical cell and an outer cell which covers the other like a bell ; the latter then divides by a 

 circular wall into an upper cell like a lid and a lower cell which is a hollow cylinder ; thus the 

 entire wall is formed of two cells. It is the same in Ceratoptcris ; in other cases, as in Asplcninin 

 alatinn, a funnel-shaped wall arises in the hemispherical mother-cell of the antheridium, the wider 

 end of which lies against the arched wall of the mother-cell ; the upper part of the cell is cut off by 

 a horizontal transverse wall to form a lid ; two or even three funnel-shaped walls may be formed one 

 after the other, so that the wall of the antheridium is composed of two or three cells running ob- 

 liquely round it and lying one above the other and of the lid-cell, as in Fig. 150. The formation of 

 the wall of the antheridium in Osmunda is quite different ; it consists below of from two to three 

 cells, surmounted by several upper cells which have proceeded from the division of the lid-cell 

 (Kny, as cited on p. 197). 



