VI] 



SEGMENTATION IN EUSPORANGIATE FERNS 



first cleavages of the embryo, and it may be held as a regular character of 

 these more delicate types of Ferns. 



But there are other Ferns of a more robust type. They are designated 

 Eusporangiate because their sporangia spring not from a single cell with 

 simple cleavages, but from a group of cells with more complex cleavages 

 (Fig. io6,£-). Moreover this exemplifies their vegetative construction also, 

 which is in all their parts more massive than that of the Leptosporangiates. 

 Since the sporangium may be held as an index of the general construction, the 

 question at once arises whether they differ also from the Leptosporangiate 

 Ferns in the structure of their growing points. The Ferns in question are 

 the Marattiaceae and Ophioglossaceae, while associated with them as inter- 

 mediate in character are the Osmundaceae. The latter may be taken first. 

 At once it is to be noted that the large sporangium cannot always be referred 



Fig. 107. Young leaf of Ceratopteris, in sur- 

 face view, after Kny ; showing two-sided 

 apical cell, and the marginal series con- 

 tinuous round the young pinnae. The 

 latter do not coincide individually with 

 the segments from the apical cell. 



Fig. 108. Apex of leaf of Osmunda, 

 showing the three-sided apical cell 

 in its relation to the two latest 

 pinnae. ( x 26.) 



wholly to a single parent cell. It shows cleavages sometimes more nearly of 

 the Leptosporangiate, sometimes of the Eusporangiate type (Fig. 106, e,f). 

 As to the apical points, the massive axis shows a three-sided conical cell 

 comparable to that of other Ferns (Fig. 10, p. 9). But the leaf both in Osmunda 

 and Todea has a three-sided instead of a two-sided initial, so placed that 

 one row of segments forms the adaxial side, the other two the abaxial flanks 

 of the leaf (Fig. io8). This more complex segmentation of the Osmun- 

 daceous leaf accords with its more robust construction. It also is winged, 

 though the wings are not produced from the middle region of each of two 

 rows of marginal cells. Here two of the three rows of segments contribute 

 to each of the wings. Transverse sections of the developing wing reveal no 

 marginal series as in Leptosporangiate Ferns, but a small-celled meristem 



