234 



REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



other object than the admission of the anthe- 

 rozoids. 



fig. 157. 



Archegonium of the same, 300 diam. 



a, origin of the archegonium ; the shaded vertical 

 row of cells constitutes the rudiment of the organ ; 

 b, archegonium immediately before impregnation. 



6 1. Second period. Fructification of the ar- 

 chegonia. In the greater number of archego- 

 nia, development ceases at the point above 

 described. In those in which the germ-cell 

 has received the influences necessary for its 

 fructification, this last-named body enlarges 

 rapidly, and very soon divides by a slightly 



Fig. 158. 



Archegonium of the same immediately after impregna- 

 tion. The germ-cell has divided by an oblique 

 septum. 



oblique septum, which is followed by a number 

 of others, alternately inclined in opposite 

 directions. This results in an egg-shaped 

 body, perfectly separable from the surround- 

 ing tissues. The last-formed summit-cell now 

 divides by a septum which is inclined not in 

 the opposite direction, but in a direction at 

 right angles to that of its predecessor. This 

 is followed by a second in the same relation ; 

 that by a third, and so on continuously. The 

 cylindrical rudiment now consists of four 

 columns of cells, each of which is divided 

 symmetrically by a vertical septum, into an 

 external trapezoid and an internal three-sided 

 cell. The former again divides, first, by a ver- 

 tical, then by a horizontal septum, both of 

 them perpendicular to the surface of the rudi- 

 ment, which now consists of four central cel- 

 lular columns, which are enclosed in eight 

 others formed of trapezoidal cells. These 

 last divide by vertical septa, alternately paral- 

 lel and perpendicular to the external surface, 

 by means of which the rudiment gradually 

 thickens. This process goes on much more 

 actively at the lower than at the upper or 

 middle portion, in consequence of which it 

 becomes club-shaped ; its swollen base being 



embedded in the parenchyma of the stem of 

 the parent, and causes absorption of its cells. 

 The cells in the neighbourhood of the ori- 

 ginally six-sided canal leading to the germ, 

 have in the meantime rapidly multiplied. 

 The upper part of the canal now encloses the 

 growing extremity of the rudiment, which, 

 however, is separated from it by a quantity of 

 fluid. It opens at the apex of a nipple-shaped 

 projection of the upper surface of the frond, 

 by a narrow aperture through which the coni- 

 cal upper extremity of the rudiment protrudes, 

 and, as it rises, usually carries with it the 

 remains of the cells immediately surrounding 

 the narrow channel through which it has forced 

 its way. .It now presents the horn-like form, 

 characteristic of the mature fruit, from which 

 the generic name of Anthoceros is derived. 



62. Changes preparatory to the development 

 of the spores. An axile cylindrical column, 

 consisting of four cellular piles, becomes dis- 

 tinguished from those surrounding it by the 

 cessation of the division of its cells by hori- 

 zontal septa. In the layer which immediately 

 surrounds it, on the contrary, division by hori- 

 zontal septa occurs twice as frequently as in 

 any other portion of the fruit. The hitherto 

 homogeneous parenchyma becomes in con- 



Fig. 159. 



Section of half-ripe fruit of the same, 120 diam. 



The axile column of elongated cells is the columella. 

 Next to it are two dark spaces corresponding to 

 a cavity, which contains at its upper part parent 

 cells of spores and elaters, inferiorly the tubular 

 cells from which they originate ; a, capsule. 



sequence distinguishable into three portions 

 an external, of about five concentric 

 layers of trapezoidal cells (the future capsule), 

 an axile portion of elongated columnar cells 

 (the future columella), and, interposed be- 

 tween these, a gingle layer of tabular cells, 

 whose greater surfaces are horizontal (the 

 cells from which are formed the spores and 

 elaters). 



63. Development of the spores. Those of the 

 cells last mentioned, which are destined to 

 become the mother-cells of spores, soon be- 

 come detached from their neighbours, and 

 assume a spherical form. Each at first con- 

 tains a large central nucleolated nucleus, and 



