REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



sacculi blended together by their smaller ends 

 in such a manner that their axes meet at a 

 central point, each forming with all the rest 

 angles of 120. The cell-wall now becomes 

 thickened by the deposition of a granular 

 material on its inner surface, which takes 

 place most rapidly along the linear ridges 

 which separate the sacculi. [n thi manner 

 six imperfect dissepiments are formed, which 

 stretch from the ridges towards the centre, 

 and encroach so far on 'the central cavity, that 

 it now communicates with the cavities of the 

 sacculi only by four narrow circular channels. 

 These changes are followed by the formation in 

 each sacculus of a delicate vesicle (the spore) 

 completely filling the cavity of each. No 

 sooner has this taken place than those por- 

 tions of the parent cell which correspond to 

 the sacculi dissolve and disappear, the four 

 oval spores remaining attached for several 

 days to the still permanent tetrahedral cen- 

 tral portion, which consists of vitreous cellu- 

 lose. The central nucleus of each spore now 

 disappears, and is replaced by two others, 

 around which the mucous and chlorophylle 

 granules group themselves. A septum is 

 soon after formed between them, dividing the 

 spore into two halves, in each of which the 

 process is repeated. In the meantime the 

 coloured external membrane is secreted on its 

 external surface. The ripening of the capsule 

 and consequent scattering of the spores takes 

 place in spring, a year after the development 

 of the archegonium within which the fruit 

 originated. 



71. Our limits will not permit us to enter 

 upon the history of the development in 

 other families of Hepaticae. In the higher 

 Jungermannias, which are provided with a 

 distinct stem, as well as with regularly formed 

 and symmetrically arranged leaves, it closely 

 corresponds to that of Pellia. In the Mar- 

 chantias, in which we have again a frondose 

 stem, we have considerable differences. The 

 antheridia are found on special receptacles of 

 various forms, sometimes stalked capitula, 

 concave superiorly, like the stalked apothecia 

 of some Lichens (Marchantia polymorpha), 

 sometimes sessile. However much the 

 general form may vary, they agree in their 

 relation to the antheridia. These last are 

 flask -shaped bags, and always completely im- 

 mersed in the parenchyma subjacent to the 

 upper surface of the receptacle. This surface 

 is always found to be scattered over with 

 nipple-shaped elevations. At the summit of 

 each an aperture is observable the termina- 

 tion of the long and narrow neck by which 

 the cavity of the antheridium communicates 

 with the surrounding medium. The fully 

 formed antheridium consists of a central mass 

 of quadrangular cells, which, surrounded by a 

 single layer of others much larger and of a 

 tabular form, is continued upwards so as to 

 form the narrow neck ; the whole being 

 closely invested by the parenchyma of the 

 receptacle. Within each of the central cells 

 is found a lentil-shaped vesicle containing a 

 spiral filament, which only differs from those 



237 



described already in its greater minuteness. 

 The archegonia of Marchantia are produced 

 on the under surface of a somewhat umbrella- 

 shaped, deeply lobed, stalked receptacle. This 

 body corresponds in the mode in which it 

 takes its origin from the notch in the anterior 

 margin of the frond, with the ordinary vege- 

 tative shoot, of which it is obviously a modifi- 

 cation. Its development has been well de- 

 scribed by M. Mirbel.* The structure of the 

 archegonium, and the commencement of the 

 development of the fruit, correspond very 

 closely with what has been described in Pellia. 

 The mode of formation of the spores and 

 elaters differs, however, considerably. The 

 latter, which in thelast-named plant, are nothing 

 more than fusiform septate cells, attain in 

 Marchantia, as well as in many Jungermanniae, 

 a more complicated structure. Their develop- 

 ment has been described in an admirable con- 

 tribution by Mr. Henfrey, who finds that the 

 young elaters are, like those of Pellia, elon- 

 gated fusiform tubes, and contain at first only 

 colourless protoplasma.-j- Soon after starch 

 granules are deposited in their interior, and 

 they are converted by a growth which is much 

 more rapid in length than in breadth, into 

 very slender, hollow filaments, attenuated at 

 each closed extremity. Still later, the starch 

 and protoplasma disappear, and at length 

 faint streaks, denoting the nascent fibres, are to 

 be perceived upon the walls. These become 

 gradually more and more distinct, till, in the 

 mature elaters, they present themselves as 

 strong flattened bands. In Marchantia there 

 are two fibres, which coil in opposite direc- 

 tions, and are confluent by their ends at the 

 extremities of the tubes in which they are 

 contained. At the time of the scattering of 

 the spores the cell-membrane gives way, and 

 the elastic fibre rapidly uncoils, at the same 

 time lengthening considerably. The parent 

 cells of the spores in Marchantia are also, at 

 an early period, fusiform. They are arranged 

 side by side with the young elaters, from 

 which they differ in being very much broader. 

 Each of these cells is converted, by the forma- 

 tion of transverse septa, into a series of four, 

 which afterwards separate from each other. 

 In each of the new cells, the protoplasma in- 

 creases in quantity and assumes a yellow 

 colour. Still later it begins to accumulate 

 into four distinct masses, each of which be- 

 comes invested in a cellulose membrane, and, 

 after the solution of the membrane of the 

 parent cell, assumes the structure and appear- 

 ance of the ripe spore. 



72. Mosses. The Mosses are distinguished 

 from the leafy Hepaticae, first, by differences in 

 the structure and arrangement of the stem and 

 leaves, involving greater complexity ; secondly, 

 by the fact that the leafy axis is not developed 

 directly from the spore, but, with the inter- 

 vention of a confervoid structure (proto- 



* Recherches Anat. et Phys. sur le Marchantia, 

 Mem. de 1'Acad. v. xiii. p. 380. 



t Transactions of Linnoean Society, vol. xxi. 

 p. 106. 



