EMBRYOLOGY 



649 



absent as a matter of fact in many of the Simplices in their mature state, 

 and apparently from all Ferns in the first condition of the seedling. 



The vascular structure thus held to be primitive and typical for Ferns 

 is that characteristic of strobiloid plants, and it seems reasonable to read 

 the anatomical data as indicating that the Ferns also are essentially 

 strobiloid, but have progressed to a condition of megaphylly, while the 

 anatomical characters that ultimately accompany that habit lagged behind 

 in the several evolutionary series, and only become apparent in the later 

 representatives of each. 



EMBRYOLOGY. 



The primary embryology of Ferns shows so nearly a dead level of 

 uniformity that it has not seemed necessary to describe the details for 

 the successive families. There are, however, two distinct types : that of 



Transverse sections through growing point of root in Osmundaceae. AOsmunda 

 regalis ; the section shows a three-sided initial (.r), but the segments are not regular, 

 ^^shows transverse section immediately below the root-cap; three initials (x, x) are 

 present ; the dotted line is the cell-division in the root-cap, seen on focussing deeply into 

 the hand-cut section ; this shows that the section has traversed the initials and is not 

 below them. C= Todea barbara, showing a very regular meristem of the root, with four 

 initials (x, x). X 144. 



the Marattiaceae, and that of the main series of the Leptosporangiate Ferns, 

 and these must be compared. The most obvious difference lies in the 

 fact that the seedling of the Marattiaceae perforates the prothallus, and 

 emerges with an upright axis through its upper surface (see Fig. 292, p. 527) : 

 that of the Leptosporangiate series emerges on the lower surface, and the 

 axis is at first prone (see Figs. 14, 15, pp. 30, 31). This difference may 

 be referred back to the first segmentation of the zygote, and appears to be 

 closely related to the difference of polarity then initiated ; for in the 

 Marattiaceae the first wall appears at right angles to the axis of the 

 archegonium, but in the Leptosporangiates it is approximately in a plane 

 including the axis. The further segmentation, and the relation of the 

 parts of the embryo, to the first divisions are substantially alike in both : 

 except that in the Marattiaceae, as also in the Osmundaceae, there is a 

 less regularity in the later divisions than is the case with the other Lepto- 

 sporangiate Ferns. In this respect Osmunda occupies an intermediate 

 position between the latter and the Marattiaceae. The parts formed in 



