REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



240 



and take their origin as follows. A hemisphe- 

 rical projecting portion of one of the superfi- 

 cial cells is cut off from the rest by a horizon- 

 tal septum as in Anthoceros. This is divided 

 by a single transverse septum. In the result- 

 ing terminal cell a second septum is formed, 

 inclined to the horizon at a small angle, which 

 is followed by a third, inclined in the opposite 

 direction. Both of the cells resulting from 

 these divisions, and subjacent to the last-formed 

 septa, are again divided by perpendicular septa 

 coinciding with the axis of the papilliform 

 rudiment. In one of the resulting cells there 

 is then formed a perpendicular septum, which 

 meets its predecessor at an angle of 45. 

 Hence results a club-shaped body, consisting 

 of a four-sided central cell, filled with granular 

 mucus, and enclosed by six others, having the 

 following arrangement. Four of the form of 

 segments of a hollow cylinder, which are in 

 contact by their edges, surround the central 

 cell on all sides. It is surmounted by a fifth, 

 which is hemispherical (the terminal cell last 

 formed). A sixth, the cell resulting from the 

 first division by a horizontal septum, is cylin- 

 drical, and serves as a pedicle on which the 

 whole is supported. The central cell is con- 

 verted by a successive division into a round 

 group of dice-shaped cellules, in the interior 

 of each of which a delicate lenticular vesicle 

 is formed, which contains, rolled up in its in- 

 terior, a spiral filament. The ripe antheridium 

 bursts at its summit, and the escape of its 

 contents is, as in the preceding cases, followed 

 by the bursting of the vesicles, and the com- 

 mencement of the active motions of the spiral 



Fig. 168. 



Aniheridia of Pteris aquilina, 260 diam. 



On the right is seen an antheridium from which 

 cells containing antherozoids are escaping; in 

 the centre another, which has not yet burst ; on 

 the left a third, which has already discharged its 

 contents. (Thuret). 



filaments (antherozoids.) In each filament 

 the extremity which is directed forwards du- 

 ring motion, is broader than any other part, 

 while the opposite extremity (posterior) tapers 

 off into a long filament. The anterior coil of 

 the spiral bears on the surface furthest from its 

 axis a number of delicate cilia. The motion of 



the antherozoid is of two kinds of progression 

 and of revolution round the axis of the spiral. 



81. The archegonia. At a period somewhat 

 later than that at which the rudiments of the 

 antheridia begin to appear, there commences 

 on the inferior aspect of the prothallium, and in 

 the immediate neighbourhood of the notch by 

 which its anterior margin is bisected so as to 

 form two lobes, an active development of new 

 cells. The result of this is the formation of 

 a cushion-like projection of the surface bor- 

 dering the notch above mentioned, upon the 

 anterior aspect of which the archegonia are 

 formed. 



82. Each archegonium takes its origin from 

 a cell, which is distinguished from those sur- 

 rounding it by the comparative abundance of 

 granular mucus which it contains, and by the 

 presence of a distinct central vesicular nucleus. 

 This cell divides by a horizontal septum into 

 a superior and an inferior portion. It is from 

 the latter, which is hemispherical, that the 

 papilla which forms the rudiment of the pro- 

 jecting portion of the organs is formed. It 

 consists, as in theHepaticae and Mosses, of four 

 contiguous columns of cells, each of which is 

 a half segment of a cylinder, the whole being 

 surmounted by a hemispherical terminal cell. 

 In the further development, varieties are often 

 observed, even on the same prothallium. 

 This is dependent on the mode in which 

 the canal occupying the axis of the mature 

 archegonium is produced. Most frequently 

 a central column of cells is formed in exactly 

 the same manner as an Anthoceros. The cells 

 forming it are afterwards absorbed and dis- 

 appear, leaving a four-sided canal. In the 

 other case, the canal results simply from the 

 separation of the four piles of cells along their 

 common line of contact. This is the arrange- 



Fig. 169. 



Archegonivm of Aaplenium septentrionale, 250 diam. 



a, germ-cell enclosed in its parent-cell; the mem- 

 brane of the latter is still perfect, and separates 

 its cavity from b, the axial canal. (Hofmeister.) 



ment which occurs constantly among the 

 Equisetaceae, Lycopodiaceae, and Rhizocar- 

 peas. In reference to the mode of origin of 

 the germ-cell, there is some difference of opi- 

 nion. According to Hofmeister,* the cell 

 which contains it originates by the formation 

 of a tangental septum in the lowest of the 

 cells, constituting one of the four columns of 



* Loc. cit. p. 80. 



