XIl] 



DISINTEGRATION OF THE SORUS 



231 



doubted that this genus is a Blechnoid derivative, and that its peculiar sori 

 arose by dismtegration of the fusion-sort of the Blechmim type, following on 

 a broadening of the sporophyll. Such examples show that the individuality 

 of the sorus is not constantly maintained, fissions and fusions being of 

 frequent occurrence. 



Fig. 229. Tortion of leaf of BlechiuiDt pmictulatum, Sw. var. 

 Krebsii, Kunze. Photograph slightly enlarged so as to show the 

 soral arrangements. 



Another way in which the individuality of the sorus may be obliterated 

 is by the spread of the production of sporangia over the free area of the 

 sporophyll. The sporangia are not always restricted to a placental region 

 above the veins, but they may appear between the veins, even covering the 

 whole leaf-surface. This may go along with a disappearance of the indusium. 

 The condition is described as " acrostichoid" and the Ferns showing it used 

 to be grouped under the generic name of Acrostidmm. It is, however, 

 palpable enough that the Ferns so grouped were diverse in their characters. 



