216 ORIGIN AND RELATIONSHIPS OF THE EUSPORANGIATAE 



The Ophioglossaceae and Marattiaceae are alike in the absence of any mechan- 

 ical tissues in the cortex of the sum. Sclerenchyma, which is well developed in 

 the leaves of most of the Marattiaceae, seems to In- entirely wanting in all of the 

 Ophioglossaceae, but the collenchyma which replaces sclerenchyma in certain 

 organs of the Marattiaceae, and is the only form ot mechanical tissue in Kaulfussia, 

 is occasionally found in the ( Ophioglossaceae. A notable case of this is the broad and 

 very conspicuous zone of collenchyma surrounding the root bundle in Ophioglossum 

 palmatum. The mucilage ducts so characteristic of Marattiaceae are apparently 

 quite wanting in all of tin < Ophioglossaceae, and the tannin sacs which are a nearly 

 constant feature in the Marattiaceae are absent in Botrychium and Ophioglossum, 

 but occur in Helminthostachys. 



In the general structure of the vascular bundles there are important resem- 

 blances. In both families the first-formed tracheids in the young sporophyte are 

 all of the short, reticulate form, and this is retained permanently in Ophioglossum, 

 but is replaced later by pitted tracheids in Helminthostachys and Botrychium. 

 Helminthostachys alone among the Ophioglossaceae shows spiral protoxylem ele- 

 ments like those found in the later bundles of the Marattiaceae. 



It is probable that the collateral bundles of Ophioglossum represent the prim- 

 itive type from which the concentric type found in the Marattiaceae has been derived. 

 In Botrychium and Helminthostachys, while the collateral type of bundle is found 

 in the stem, in the petioles the bundles are concentric, as they are in the Marattiaceae. 

 The collateral type of bundle reappears again in the early stages of the sporophyte 

 in Datnvu. 



Angiopteris, which is probably the most specialized of the living Marattiaceae, 

 has concentric bundles only. 



