REPRODUCTION, VEGETABLE (VEGETABLE OVLM). 



ever, examples frequently occur, in which its 

 development is changed, under the influence 

 of peculiar external circumstances, in such a 

 manner that, instead of producing a sporan- 

 gium it lengthens considerably, and bears 

 symmetrically arranged leaves. Such a con- 

 dition makes" it more easy to compare the fruit 

 of the Mosses and the leafy stems of the 

 higher plants. In the Ferns and Equisetaceae, 

 again, only one transverse septum is formed; 

 but here, it is the inferior secondary cell 

 which is developed to the embryo, the 

 direction of the first axis of growth being 

 opposite to that of the archegonium. In 

 Selaginella, a succession of transverse septa 

 are formed, whence results a conferva-like fila- 

 ment, which lengthens downwards by repeated 

 division of a terminal cell. At length the 

 youngest cell is transformed into an embryo. 

 Among the Coniferae, the same process pre- 

 sents itself, with this important difference, that 

 before it commences, the germ divides by two 

 crucial vertical septa into four cells, which 

 correspond to the four embryos which are 

 afterwards formed. In all the Phanerogamia, 

 probably without exception, the germ-cell 

 divides," in the first instance, by a trans- 

 verse septum into two cells, of which the 

 upper is the larger. In some cases the lower 

 cell is developed directly to a spherical cel- 

 lular mass (as in Hippuris and Orchis Morio). 

 Much more frequently, however, it is trans- 

 formed into a conferva-like filament (sus- 

 pensor) which lengthens by repeated division 

 of an inferior terminal cell. At length the 

 youngest cell, instead of lengthening, becomes 

 spherical, and gives rise to the embryo by a 

 process similar to that described above in 

 Hippuris. 



1 15. The organ to which the name suspen- 

 sor is applied by Mr. Henfrey in Orchis Morio, 

 differs materially from that of Selaginella, the 

 Coniferse, or from that described in the pre- 

 ceding paragraph. Its formation does not, like 

 that of the true suspensor, precede, but follows 

 the origin of the embryo. In Hippuris, it 

 appears to result from endogenous cell-forma- 

 tion in the lengthened upper compartment of 

 the original germ-cell. 



116. The difference bet ween the development 

 of the pollen grain, and that of the microspore 

 of Selaginella and of the Rhizocarpeae, is no 

 less remarkable. Among the Phanerogamia, 

 after the pollen grain has remained for some 

 time in contact with the stigma, its inner mem- 

 brane grows out at one point of its periphery 

 into a filiform cell ; this lengthens more or less 

 rapidly until it reaches the micropyle of the 

 ovule, which it enters, and at last comes into 

 contact with the embryo sac. The sac 

 usually resists it strongly ; sometimes it is 

 bulged in, but is very rarely perforated. In 

 consequence of this act the transformation of 

 the germ-cell commences. The absence of 

 moving filaments among the higher plants 

 stands connected with the intervention of a 

 second membrane (that of the embryo sac) 

 between the two fluids, the union of which 



! 253 



seems to constitute the essential condition of 

 fecundation. 



117. In comparing the development of the 

 microspore with that of the spore of the Ferns 

 with which the plants among which it presents 

 itself are so closely allied, the difference is 

 even more striking. In Selaginella all the 

 steps intervening in the Fern between the 

 spore and the tessellar cells of the antheri- 

 dium have disappeared. 



1 18. Direct observations relating to the act 

 of impregnation among the Cryptogamia, are 

 for the most part wanting. The presence of 

 antherozoids in the cavities of the archegonia 

 of the Ferns has been witnessed only by Su- 

 minski and Mercklin. Among the Hepaticae 

 and Mosses, Hofmeister observed within the 

 involucre of Jungennannia bivaricata,anthero- 

 zoa " which moved rapidly and played livelily 

 round the archegonia."* In this species, as 

 well as in J. bicrenata and bicuspidata, the 

 same observer found a mucous substance of 

 glass-like transparency, occupying the mouths 

 of the archegonia. In this substance were 

 embedded numerous curled fibres, which he 

 considered to be dead antherozoids. Evi- 

 dence more to be depended upon is that of 

 the concurrent testimony of all observers 

 that, among the dioecious mosses and liver- 

 worts, wherever plants bearing archegonia 

 grow in the neighbourhood of those bearing 

 antheridia, fruits are almost always produced ; 

 while in the contrary case, the archegonia are 

 abortive. 



119. Origin and development of germ-cells in 

 special organs destined for their reception, which 

 are capable of transformation into rudiments of 

 new plants, without the concurrence of two organs 

 of opposite functions. Of this, distinct ex- 

 amples occur only among the Hepaticae ; viz. 

 among the leafy Jungermanniae, and the 

 Marchantiae. In one of the latter, the Lumtlaria 

 vulgaris, there is formed by the doubling in of 

 the epidermal layer of the upper surface of 

 the frond, immediately behind the notch in the 

 anterior margin, a crescentic pouch, which 

 extends backwards for about a line under the 

 surface. Its cavity is bounded by an inferior 

 and a superior wall, whose concave surfaces 

 unite in a sharp margin, the plane of which 

 inclines slightly backwards and downwards. 

 The upper wall is formed by the double epi- 

 dermal membrane ; the lower by a membrane 

 which is intimately united with the parenchyma 

 of the frond, in its relations to which it re- 

 sembles the tissue which lines the subepider- 

 mal air cavities. It consists originally of a 

 single layer of tessellar cells, much smaller 

 than those upon which they are supported. 

 A number of these grow out into papilliform 

 projections, in each of which the projecting 

 hemispherical portion is soon separated by a 

 transverse septum. A second is then formed 

 above the first, and parallel to it. The highest 

 cell next divides by a vertical septum parallel 



* Hofmeister, Yergleichende Untersuchungen, 

 &c. S. 38. Vide supra, Fig. 164. 



