REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



252 



layer consists of radiating prismatic cells, and 

 is soon absorbed. The cells of the second 

 layer are distinguished by their containing at 

 first numerous starch grannies, and afterwards 

 by the deposition of spiral fibres on the inner 

 surfaces of their walls. These are usually 

 dice-shaped cells arranged in concentric 

 layers. The external or epidermic layer 

 consists of tabular cells in contact by their 

 edges.* 



1 10. Review of the analogies which present 

 themselves in the history of the development of the 

 reproductive organs of I he higher Cryptogamia and 

 of the Phanerogamia. The families in question 

 are distinguished by the presence of what is 

 called "sexual reproduction" from aH others. 

 It is true that among the Characeas, Conju- 

 gata:, Vaucheriacea?, and Desmideag, the con- 

 currence of two dissimilar parts is necessary 

 for the development of the germ ; but in them 

 the phenomena do not present themselves in 

 such strict conformity to law, and the anato- 

 mical relations of the germ to the organ which 

 contains it are not nearly so complicated _ as 

 in the plants under our consideration. Taking 

 the sexual germ as our starting point, in com- 

 paring the history of the development of the 

 phanerogamous with that of the cryptogamons 

 plant, the following analogies present them- 

 selves : 



1 11. 1. Analogies existing between the ovule, 

 the anther, and the sporangium In Zostera 

 marina the termination of a stem destined 

 to bear reproductive organs, is broadened out 

 in the form of a spatula, concave on one side, 

 convex on the other. On the concave sur- 

 face are observed, early in the development, 

 two vertical series of papillae one on each 

 side of the middle line which are the rudi- 

 ments of the organs which support the ovules 

 and anthers. In each series, the two kinds of 

 rudiments are arranged alternately in such a 

 manner, that an ovule in one series is always 

 on the same level with an anther in the other. 

 The rudimentary organ which is destined to 

 contain the ovule, commences as an imperfect 

 ring of cellular tissue, on the inside of which 

 is seen a little round projection a bud in 

 the axil of a leaf. From this projection is 

 developed the ovule, with its teguments, just 

 as described in Orchis Morio. The axis of 

 its nucleus is occupied by a vertical series of 

 cells. Of these the uppermost enlarges, and 

 becomes detached from its neighbours, so as 

 to form the embryo-sac.-)- If we compare this 

 process with what occurs in Selaginella, we 

 find in each case, a cell belonging to the stem 

 in the axil of a modified leaf, which transforms 

 itself into an axial organ. In each case one 

 of the central cells enlarges and becomes 

 djtached in Selaginella, to form the mother 



* Nageli, Zur Entwick. des Pollens, &c. Zurich, 

 1842 ; Wimmel, Zur Entwick. ties Pollens, &c. Bot. 

 Zeit. 1850. S. 225. 



+ Hofmeister, Entwick. der Zostera. Bot, Zeit. 

 1851 ; Gronland, Beitrag. zur Kcnnt. der Zostera 

 marina, &c, Bot. Zeitung, St. 10. 1851. 



cell of four spores in the phanerogamous 

 plant, to become the embryo-sac. 



112. The exact correspondence, step for 

 step, which exists between the development of 

 the anther, and that of the sporangium, will be 

 best seen by successively comparing the de- 

 scriptions contained in 89 and y 108. It is 

 rendered still more striking when we consider 

 the very remarkable variations which present 

 themselves in the structure of the anther 

 among the Phanerogamia themselves ; as e. g. 

 in Zostera, among the Orchidaceae, and other 

 examples for the description of which space is 

 wanting. The contemplation of these analo- 

 gies leads us to remark how little relation there 

 seems to be as respects the organs under con- 

 sideration between the morphological import 

 of the rudiment and its development. The 

 ovule of Zostera is an axial organ, originating 

 in the axil of a modified leaf; its analogue in 

 development, the anther, is itself a bilateral 

 foliar organ. The sporangium of Equisetum 

 seems to originate as a leaf, that of Selagi- 

 nella, as an axis in the axil of a leaf. 



1 13. 2. Analogy between the embryo-sac, the 

 pollen cell, and the parent cell of four spores 

 In approaching this, the most difficult part of 

 our inquiry, we must refer to the Coniferae, as 

 holding in so many respects an intermediate 

 position. Of those stages of the development 

 which precede the act of impregnation in Se- 

 laginella, the first, namely, the division of the 

 parent cell into four compartments, and the 

 formation of a spore in each, is entirely wanting 

 in the Coniferae. The prothallium under- 

 standing by the term the organ of which the 

 archegonia form a part is represented by the 

 corpuscula, between which and the archegonia, 

 the resemblance in structure is very striking. 

 The difference in the mode of origin of the 

 germ-cell, on the other hand, is no less re- 

 markable. " Among the Cryptogamia there is," 

 says Hofmeister, " only one germ-cell which 

 completely fills the central cell of the arche- 

 gonium, while in the Coniferae, very numerous 

 germ-cells swim in the central cell of the cor- 

 pusculum, of which one only, applied against 

 its lower end, is fecundated." In the gymno- 

 spermous Phanerogamia, all the steps of de- 

 velopment which intervene between the parent 

 cell and the germ, disappear ; the latter origi- 

 nating altogether independently at the upper 

 end of the embryo-sac. As the transforma- 

 tion of the germ-cell is the most important 

 element in the process of development, it 

 presents the greatest degree of constancy. It 

 always commences by the formation of one 

 or more septa, the direction of which, in rela- 

 tion to that of the first axis of growth, is 

 transverse or nearly so. 



111. In the Hepaticos and Mosses one sep- 

 tum is formed, the inferior of the two result- 

 ing cells undergoing no further development, 

 while the superior is transformed into the pri- 

 mary axis of the fruit. This fruit-axis, the apex 

 of which is converted into a sporangium, is 

 normally a leafless one. In the Mosses, how- 



