THE ADULT SPOROPHYTE 85 



IV. THE ADULT SPOROPHYTE. 



The essential characteristics of the sporophyte are estabHshed while it is still 

 quite small and the subsequent differences are mainly an increase in the size of the 

 parts and finally the development of the spore-bearing structures which constitute 

 the pecuhar spike or sporangiophore so characteristic of these plants. As the 

 structure of the tissues has been repeatedly studied and described, no attempt will 

 be made here to take up a detailed study of these. 



The Ophioglossaceae in general, except for the rather elaborate vascular bundles 

 of the stem, especially in Botrychium, are marked by great simplicity in the structure 

 of the tissues. The surface is usually smooth except in the younger plants, where 

 there may be a development of scales and hairs, presumably for the protection 

 of the young tissues of the stem apex. The hard hypodermal tissues and bands 

 of sclerenchyma, so common in the leaves and stems of many ferns and developed 

 to a less degree in the Marattiaceae, are practically entirely absent from the Ophio- 

 glossaceae. 



Except for the vascular system of the stem the bundles are usually less developed 

 than is common in the more highly differentiated ferns, this being especially the case 

 in Ophioglossum, where the very delicate bundles forming the veins of the leaf run 

 through the spongy green tissue of the leaf without causing any projecting veins at 

 the surface. This condition is true also in the simpler types of Botrychium and in 

 the young leaves oi Helminthostachys. The great bulk of the ground tissue in leaf, 

 root, and stem is parenchyma. The development of periderm in the outer tissues 

 of the stem is probably always associated with the leaf bases and serves, as we have 

 seen, both to separate the dead leaf bases and to protect the scar thus left after the 

 leaf has fallen away. 



The roots are characterized by the complete absence of root hairs. The outer- 

 most layer of cells often has the walls much thickened and they may show the reac- 

 tion of cork. The bulk of the cortex of the root, however, is composed of unmodified 

 parenchyma. The vascular cylinder in the root remains monarch in the section 

 Euophioglossum, but is diarch in the smaller roots oi Ophioderma and in the smaller 

 species oi Botrychium, and ranges to hexarch in the larger roots.of Helminthostachys. 

 The roots, especially in the larger species, are thick and fleshy and as a rule branch 

 sparingly and somewhat irregularly. In the section Euophioglossum no lateral 

 roots are formed and branching is rare. When it does take place it is the result of a 

 true dichotomy of the apex. The root, as in the youngest stages in the plant, grows 

 almost always from a single tetrahedral apical cell, which is much alike in all the 

 genera. 



The most characteristic feature of the Ophioglossaceae is the peculiar sporangial 

 spike referred to. There is a certain correlation in the degree of development of this 

 spike and the sterile leaf segment with which it is associated. The fertile leaves 

 may arise very early in the history of the sporophyte. Bruchmann states that the 

 first leaf to appear above ground in Botrychium lunaria is already a fertile one and 

 in Ophioglossum vulgatum the second green leaf to be developed usually bears spores. 

 This early development of the fertile leaf is probably an indication of the primitive 

 nature of these plants, as we must assume that the ancestral form must have at once 

 developed a sporangial structure on the first leaf, or what corresponded to that in 

 the embryo. In Botrychium lunaria Bruchmann figures young spore-bearing plants 

 which are still connected with the prothallium, and Jeffrey states that in B. virgini- 

 anum he once found a fruiting plant with which the prothaUium was still connected. 



