ON THE HIGHER CRYPTOGAMOUS PLANTS. 113 



According to this author, the large spores of Selaginella invohens possess 

 two coats, each composed of two layers ; and in an early stage of the germi- 

 nation, the inner layer of the outer coat, together with the inner coat, form 

 the walls of a globular body which does not wholly fill the cavity enclosed 

 by the outermost membrane. This globular body is firmly attached to the 

 outer membrane immediately under the point of junction of the three ridges 

 separating the flattened surfaces of the inner side of the spore. The globule 

 enlarges until its walls come to be applied closely to the outer layer, com- 

 pletely filling up the large cavity. Then between the two layers of the inner 

 coat, at a point immediately beneath the point of junction of the three exter- 

 nal ridges, a process of cell-formation commences, producing a flattened plate 

 of tissue interposed between the two layers ; this structure is the pro-embryo. 

 The cells are at first in a single layer, but the central ones soon become di- 

 vided by horizontal septa so as to produce a double layer, and finally four or 

 more tiers of cells one above another. The outline of the pro-embryo, seen 

 from above, is circular, spreading over the upper part of the spore. On its 

 surface appear the so-called ovules. The first is produced at the apex of 

 the pro-embryo, the rest, to the number of twenty or thirty, arranged upon 

 its surface in three lines corresponding to the slits by which the outer coat 

 of the spore bursts. These ovules, closely resembling those of Salvinia, Pi' 

 lularia, the Ferns, fkc, consist of a globular cell surmounted by four cells, 

 which rise up into four papillae, and leave a canal or interceHular passage 

 between them, leading down to the globular cell or embryo-sac. The four 

 cells are usually developed into four or five cells, one above the other, by 

 the production of horizontal septa ; sometimes they are developed unequally 

 and to a considerable extent so as to form papillae, presenting an orifice be- 

 tween them at some point on the outer surface, indicating the canal leading 

 down to the embryo- sac. 



During the development of the ovules, a delicate parenchyma is produced 

 in the great cavity of the spore, finally entirely filling up this spore. 

 Before it has completely filled it, the embryo makes its appearance in the 

 embryo-sac of one of the ovules. 



The first change in this sac is the appearance of a nucleus ; from this cells 

 are developed representing the suspensor of the embryo. The cells of the 

 suspensor multiply and form the process which penetrates down into the 

 parenchyma of the cavity of the spore ; at the lower end may be detected 

 the embryo, a minutely cellular body. Dr. Mettenius never saw the embryo 

 produced in the embryo-sac before the suspensor had broken through the 

 bottom of it to penetrate the parenchyma of the spore-cell ; it was always 

 within this parenchyma and attached to the end of the suspensor. In this point 

 he is decidedly opposed to Hofmeister, who states that the embryo originates 

 in the embryo-sac, whence a young embryo attached to its suspensor may 

 easily be extracted from the spore. 



The part of the embryo opposite to the point of attachment of the suspen- 

 sor corresponds to the first axis of the Rhizocarpeae, which never breaks out 

 from the spore-cell in Selaginella ; it pushes back the loose parenchyma of 

 the spore- cell as it becomes developed, and when completely formed, is sur- 

 rounded by a thin coat composed of several layers of the parenchymatous cells 

 much compressed, enclosed in the still existing inner coat of the spore. On 

 one side of the point of attachment of the suspensor the embryo grows out 

 towards the point where the spore-cell has been ruptured, thus apparently 

 in a direction completely opposite to the end of the axis. As it enlarges it 



1851. I 



