REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



236 



of the young shoot. Soon after their origin, 

 there is formed, by the continued growth of 



Fig. 163. 



Antherozoids of PeUia, 400 diam. (Thuret.) 



the shoot below them, a thin laminar prolong- 

 ation upon the surface of which they are sup- 

 ported. By a process of cell-division resem- 

 bling that observed in the development of the 

 antheridia of Anthoceros, each rudiment is 

 converted into a cylinder, rounded above 

 and consisting of a single central cellular 

 column, surrounded by a single layer, which 

 is formed of four perpendicular series of 

 flattened cells in contact with each other 

 by their edges. The cells of the central 

 column contain granular mucus, in which ve- 

 sicular nuclei are embedded. As the arche- 

 gonium becomes fully formed, the lowest cell 

 in the series, as well as its nucleus, enlarges, 

 and the cells of the outer wall in its neigh- 

 bourhood rapidly multiply, so that the organ 

 becomes swollen out at its lower part. The 

 development is completed by the disappearance 

 of the transverse septa, which separate the 

 cavities of the cells forming the central 

 column. In this manner is produced an 

 axile channel, closed above, and terminating 

 below in a flask-shaped dilatation, in which 



Fig. 164. 



Archegonium of Jungermannia bivaricata at period 

 of impregnation, 400 diam. 



Cellules containing antherozoids are observed at 

 the entrance of the canal. 



the enlarged nucleus of the basal cell (germ- 

 cell) is contained. Soon the cells forming 



the summit of the archegonium give way, so 

 as to open a communication between its cavity 

 and the external atmosphere. 



69. Second period. Development of the em- 

 bryo. In consequence, as there is every reason 

 to believe, of the entranceof the spiral filaments 

 into the cavity of the archegonium, the germ- 

 cell is divided by a tranverse septum into a 

 larger inferior and smaller superior (hemi- 

 spherical) portion. This last next divides by 

 two perpendicular septa crossing each other 

 at right angles, which are succeeded by a 

 third, which is horizontal. This is succeeded 

 by others parallel to it, each new septum being 

 placed immediately above its predecessor. 

 Hence results a cellular cylinder, the rounded 

 summit of which always consists of four cells, 

 divided from each other by crucial septa. By 

 successive cell-divisions, this body becomes a 

 pear-shaped cellular mass. Afterward by the 

 lengthening of its middle third, the cylindrical 

 stalk of the perfect fruit is formed, and still 

 later from the lower third springs a cup- 

 shaped sheath, the margin of which reaches 

 to about a third of the length attained by the 

 stalk of the fruit before it has escaped from 

 its calyptra. 



70. Changes preparatory to the development 

 of the spores. At an early period, when the 

 young fruit is still pear-shaped, its rounded up- 

 per end (the future capsule) manifests peculi- 

 arities in its intimate structure. The cells of its 

 superficial layer are divided repeatedly by 

 septa perpendicular to the surface, while those 

 which they enclose gradually enlarge without 

 dividing. The result of this process is the 

 formation of a central mass of large dodecahe- 

 dral cells (parent cells of the spores and 

 elaters), which is surrounded by a single layer 

 of tabular cells of not more than a quarter 

 their breadth (the future wall of the capsule). 

 As the development proceeds, the walls of the 

 central cells become thickened by the deposit 

 of a gelatinous material on their internal sur- 

 faces. This material, which is coloured violet 

 by iodine, swells out, and finally dissolves, on 

 the addition of water, the globular primordial 

 vesicle, which occupies the centre of the cells, 

 being brought into view. Still later both the 

 cell membranes and their gelatinous linings 

 disappear, and the primordial membranes are 

 left, lying in the cavity of the young capsule. 

 Soon after they clothe themselves with new 

 membranes of cellulose, and assume forms, 

 which differ according as they are destined to 

 become parent cells of spores or elaters. Those 

 of the newly formed cells which are to be elaters, 

 assume the form of spindles. They are found 

 partly grouped round the axis of the capsule, 

 partly in series which radiate from it towards 

 the circumference. The future parent cells 

 retain only for a short time their globular 

 contour : soon four projections of the mem- 

 brane of each cell become visible, each of 

 which would correspond in position to one of 

 the angles of a regular tetrahedron contained 

 in the parent cell. These projections increase 

 so rapidly, that in a short time the whole 

 presents the appearance of four egg-shaped 



