594 FILICALES 



As seen from Figs. 330 B, c, the sporangial mother-cells are deeply 

 sunk, and the first segment-walls may insert themselves upon the basal 

 wall, as is shown in sporangium (3), Fig. c ; in other cases the segment 

 walls may cut the lateral walls of the mother-cell (e.g. sporangium 4). 

 But, however this may be, the first segmentations are those characteristic 

 of bulky sporangia. 



The sporangia themselves are of large size, and vary somewhat in 

 form, being in D. Citldta of an almost pear-like shape with very oblique 

 ring, while in D. Menziesii the ring is more longitudinal. The stalks 

 are relatively thick though elongated, and show in transverse section a 

 rosette of six or seven cells (Fig. 330, central drawing). As the published 

 drawings of Dicksonia sporangia are not altogether satisfactory, I have 

 represented those of D. Menziesii, Hook and Baker, from four different 

 points of view. Fig. 330 H shows how, on the peripheral face, the con- 

 tinuous ring of the annulus surrounds the relatively large thin-walled area ; 

 the indurated part of the annulus is shaded, and of the rest, four smaller 

 cells (connective cells) are seen on either side of the group of five cells 

 which form the stomium. The central face is shown in Fig. 330 F ; 

 but in this case the stomium is composed of only four cells, while five 

 connective cells are seen on either side of it. Fig. 330 E shows a lateral 

 view of the side on which the annulus is completely indurated, and Fig. 

 330 c. shows the stomium as again a group of five cells, while two pairs 

 of " connective " cells are seen on either side of it. From these drawings 

 the form and large size of the sporangium, and the position of the annulus 

 are clearly seen, while we also conclude from them that the number of 

 cells of the stomium and connective is not constant. 



The orientation of the sporangia has been examined in D. Schiedei, 

 Chamissoi and Menziesii '; at the margin of the flattened receptacle it is 

 not uniform, but the sporangia seated on the sides nearer its base show 

 in the majority of cases, though with no strict uniformity, an orientation 

 on the Gleicheniaceous plan. 



Notwithstanding the large size of the sporangia, the output of spores 

 in Dicksonia is not a high one. Enumerations were made for D. Menziesii 

 with 62, 63 as the result, and in D. antantica, 64. Clearly 64 is the typical 

 number for these Ferns. 



ANATOMY. 



The vascular system of Dicksonia can only be properly understood 

 in the light of the simpler forms, and especially of the Dennstaedtiinae. 

 Nevertheless it will be described here, and referred to again later. It 

 has been examined in D. Baromctz and Culcita by Gwynne-Vaughan, 1 

 who finds the system of the axis to consist of a cylindrical dictyostele 

 surrounding a large central pith. The meshes of the dictyostele are the 

 foliar gaps, and from the lower limit of each arises a leaf-trace in the 



1 Ann. of l>ot., xvii., 1903, p. 708. 



