D1CKSONIEAE 



593 



series of actively dividing cells. In sections perpendicular to the leaf- 

 surface the young sorus appears as in Fig. 330 A, the cell marked (m) 

 being one of the marginal series. A section of a similar sorus in a 

 plane (x, x) appears as shown in Fig. 330 D (the chain of 10 cells 

 superposed on the lip of the indusium), while at the lower level (y, y) 

 it is. as shown between the indusial lips. It is thus seen that the receptacle 

 is structurally like n normal leaf-margin, a conclusion again supported by 

 Fig- 330 B, which shows a similar sorus traversed in a plane (z, z) 



H 



FIG. 330. 



Dicksonia Schicdci, Baker. A= section through a young sorus perpendicular to the 

 leaf-surface ; z", 2 = indusium ; / = cell of marginal series. .5 = section of sorus parallel to 

 the leaf-surface as along a line z, /', in Fig. A, showing receptacle bearing sporangia s, s. 

 C = a similar section bearing older sporangia. /^ = transverse section of a young sorus 

 showing the two lips of the indusium (znd), and receptacle between them, as along a 

 plane y, y, in Fig. A. A section of the receptacle as in plane -t",.f, in A, is superposed on 

 the lower indusial lip. The central figure shows sporangial stalks cut transversely. A-D 



X 200. E) f, G, H sporangia of Dicksonia Menzicsii from four different points of view. 



Xso. 



indicated in Fig. 330 A. It is important to note the inequality in size 

 of the two lips of the indusium. Here it is only slight, but in forms to 

 be subsequently described an increasing inequality, both in area and in 

 substance, makes its appearance. The formation of the sporangia has 

 begun in the marginal cells, and it is seen that their appearance is 

 almost simultaneous, a point better shown in Fig. 330 c, which repre- 

 sents a slightly more advanced stage. These marginal sporangia are 

 succeeded by others produced in a basipetal sequence, but the succession 

 is not long continued, and in D. Culdta, L'Herit, it is not clearly marked ; 

 there is, however, no evidence of intercalation of younger sporangia 

 between those already present. 



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