282 



MOSSES AND FERNS 



CHAP. 



verse and is followed in each half by two others, the median and 

 octant walls. The nearly globular embryo is thus divided into 

 eight similar cells, each having the tetrahedral form of a globe 

 octant. The next divisions are not perfectly understood, and 

 evidently are not absolutely uniform in all cases. All the 

 octants at first show nearly uniform growth, and the embryo 

 retains its nearly oval form (Figs. 153, F, 154, A). The first 

 division in the octants is essentially the same, and consists in a 

 series of anticlinal walls, before any periclinal walls appear, so 

 that we may say that for a short time each octant has a distinct 

 apical growth, and there are eight growing points. The older 



A. 



st. 



tr 



FIG. 155. Marattia Douglasii. A, Cross-section of the young sporophyte at the junc- 

 tion of the cotyledon and stem; st, the apical meristem of the stem, Xais; B, the 

 stem apex of the same, X43o; C, longitudinal section of the stem apex of a plant 

 of about the same age, X2is; tr, the primary tracheary tissue; r 2 , the second 

 root. 



embryo shows an external differentiation into the first leaf, 

 stem, and root, but the foot is not clearly limited at first. The 

 basal wall separates the embryo into two regions, epibasal and 

 hypobasal. From the former the cotyledon and stem apex 

 are derived, from the latter the root and foot. 



The cotyledon arises from the anterior pair of epibasal 

 octants, which are in the Marattiacese, unlike all the other Ferns, 

 turned away from the archegonium opening. In the earliest 

 stages where the cotyledon is recognisable, no single apical cell 

 could be made out, and later the growth is very largely basal. 



