3i8 



MOSSES AND FERNS 



CHAP. 



of the apical cell, the originally conical leaf rudiment becomes 

 flattened, and a little later this is followed by a dichotomy of 

 the growing point and the production of two apical cells like 

 the original one (Fig. i6i, C). The division is first brought 

 about by a nearly central longitudinal division of the apical 

 cell, and on either side of this, by a curved wall running to the 

 outer wall of each cell, two new apical cells, separated by two 

 elongated central cells, result. Each of these new growing 

 points develops one of the lobes of the cotyledon, which undergo 

 one or more bipartitions before the cotyledon breaks through 



A. ^ C. 



Fig. i6i. — Onoclea struthiopteris (Hoffm). A, Longitudinal section of young sporophj-te still con- 

 nected with the prothallium (J>r), X 60 ; B, the apex of same, x 180 ; C, surface view of the young 

 cotyledon showing the first dichotomy ; D, central region of A, showing the primary tracheary 

 tissue, X180 ; E, young sporophyte with nearly full-grown cotyledon and primary root, X3 ; st, 

 stem ; L^, cotyledon ; L2, second leaf ; F, foot ; pr, prothallium. 



the prothallium. As in Marattia the growth is much stronger 

 upon the outer side and the leaf strongly curved over. It very 

 early grows beyond the stem apex, and the embryo loses its 

 oval form much earlier than is the case with any of the 

 Eusporangiatae. 



The Stem 



The early segmentation of the stem apex is much the same 

 as in the cotyledon ; but later the divisions in the segments are 



