X FIIJCINE.K LEPTOSPORANGIAT.K 331 



but in the sieve-plates callus is found. The rest of the phloem 

 is composed of conducting cells, with thin walls and oblique 

 septa. The endodermis becomes dark-coloured and its walls 

 lignified, and when the root dries the vascular cylinder often 

 becomes separated from the ground tissue by the transverse 

 splitting of the endodermal cells. 



The secondary roots arise in regular succession in two 

 lines, corresponding to the ends of the xylem plate in the 

 diarch bundle. They themselves generally branch further, and 

 thus very extensive root systems are formed. The origin of 

 the lateral roots of the Ferns has been exhaustively studied by 

 Lachmann,^ but their position seems to be of very little import- 

 ance systematically, and except in a few cases like Osnninda, 

 where two roots regularly arise for each leaf, there is little 

 relation between roots and leaves. In creeping rhizomes they 

 arise either mainly from the ventral side or from all parts 

 indifterently. As yet the only forms in which complete 

 absence of roots is known among the Leptosporangiatae are 

 Salvinia, species of TricJionianes, and Stroniatopterisf one of 

 the Gleicheniaceae. In all of these, however, there are 

 substitutes either in the form of modified leaves {Salvinia) or 

 root-like rhizomes. 



The formation of buds from the roots, such as occur in 

 OpJiioglossinn, have been also observed in some Leptosporan- 

 giatae. This was first discovered by Sachs in Platyceriuin 

 Wallichii, and later described by Rostowzew,^ and Lachmann "* 

 also describes it in Anisogoniuvi Seramporense. In all these 

 cases the apex of the root appears to become transformed 

 directly into the apex of the bud. 



TJie Sporangium 



The development of the sporangium of all the Leptosporan- 

 giatae is much the same, but the position of the sporangia, and the 

 character of the indusium when present, varies much, and will 

 be discussed later as the different families are treated separately. 



In the Polypodiaceae the sporangia, as is well known, arise 

 usually in groups (sori) upon the backs of leaves that differ 

 but little from the ordinary ones. Sometim.es, however, eg. 

 Onoclea, they are very different, the sporangia being produced 



^ Lachmann (7). - Poirault (2), p. 147. ^ Rostowzew (i). ■* Lachmann (7). 



