FERNS. 



345 



of the two daughter- cells is at once divided again by transverse septa, so that the 

 segmented oospore or embryo now consists of four cells placed as quadrants of a 

 sphere, and which are bisected by a longitudinal section. In Fig. 256 these first 

 transverse divisions are indicated by thicker Hues, the embryo being seen in longi- 

 tudinal section. The explanation of the figure points out the interpretation which 



w/i 



FtG. 256.— Vertical longitudinal section of the embryo of Pferis aquilina (after Hofmeister, Entwickelung iind 

 Bau dcr Vegctationsorgane der Fame, p. 607) : the thicker lines are sections of the first three division-walls by 

 which the embryo is divided into four cells. The lower anterior cell forn)s, according to Hofmeister, the leaf 5 at 

 the apex of the stem st; from the lower posterior cell is produced the root, stu being its apical cell and wh its 

 root-cap. In Pteris, the foot y is formed from the two upper of the first four cells. In Aspidiian Filix-mas, the 

 same author states that these processes diverge still further from those in the Rhizocarps. 



Hofmeister gives to the first four cells of Pieris aquilifia, which the reader may 

 compare with the corresponding development of Salvinia and Marsilea; but it must 

 not be forgotten that the embryo of the Fern lies, so to speak, on its back. Al- 

 though it is impossible in this place to go into a more minute description, it is 

 ,still necessary at least to point out the resemblance between the embryo of Ferns 

 and that of Rhizocarps. 



Fig. 257.— .-/<//d»w'«>« Capillus-Vencris ; vertical longitudinal 

 section through the prothallium // and the young Fern £: 

 k root-hairs, a archegonia of the prothallium, * the first leaf, 

 w the first root of the young plant (X about 10). 



FIG. ■2-^9,.—Adiantuiii CapUlus-Veneris ; the pro. 

 thallium // seen from below with the young Fern 

 attached to it ; b its first leaf; w' iv" its first and 

 second roots; /z root-hairs of the prothallium (X about 

 30). 



If we neglect for the moment the points which are still doubtful in the signi- 

 ficance of each of the first four cells of the embryo, it is certain that one of them 

 which is inferior^ and posterior becomes the mother-cell of the first root, and that 

 the apical cell of the stem lies immediately in front of and above the base of the leaf. 



* The terms posterior, anterior, superior, inferior, refer also to the prothallium, the apex of 

 which is turned in front, and its archegonia-bearing surface downwards. 



