ix FILICINE& LEPTOSPORANGIATJE 339 



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 (7), but their position seems to be of very little im- 

 portance systematically, and except in a few cases like 

 Osmunda, where two roots regularly arise from each leaf, there 

 is little relation between roots and leaves,. In creeping rhi- 

 zomes they arise either mainly from the ventral side or from 

 all parts indifferently. As yet the only forms in which com- 

 plete absence of roots is known among the Leptosporangiatae 

 are Salvinia, species of Trichpmanes, and Stromatopteris 

 (Poirault (2), p. 147), one of the Gleicheniacese. In all of 

 these, however, there are substitutes either in the form of modi- 

 fied leaves (Salvinia) or root-like rhizomes. 



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

 Ophioglossum, has been also observed in some Leptosporan- 

 giatae. This was first discovered by Sachs in Platyccrium 

 Wallichii, and later described by Rostowzew ( i ) ; and Lach- 

 mann (7) also describes it in Anisogonium Sermamporense. 

 In all these cases the apex of the root appears to become trans- 

 formed directly into the apex of the bud (Fig. 171, B). 



The 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, vary much, and 

 will be discussed later as the different families are treated sep- 

 arately. 



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. Sometimes, however, e. g., 

 Onoclea, they are very different, the sporangia being produced 

 in great numbers, and the lamina of the leaf is much contracted. 

 One of the simplest cases is seen in Polypodium. Here the 

 sporangia develop late upon ordinary leaves, and form scat- 

 tered round sori, bearing, however, a definite relation to the 

 veins in this case forming above the free end of one of the 



