THE OLDER SPOROPHYTE 187 



While mucilage ducts are present in both leaf and stem, they are less numerous 

 and conspicuous than in Danaa. There is a ring of them in the outer cortex and 

 several larger ones in the central region. Kuhn states that, although these mucilage 

 ducts sometimes look as if they were of schizogenous origin, in reality they are 

 always lysigenous, i. e., they are formed by the fusion of several mucilage-secreting 

 cells. 



In the cotyledon and the earlier leaves a section of the lamina shows, between 

 the large-celled epidermis of the upper and lower sides, a mesophyll composed of 

 about three layers of quite indifferent parenchyma, exactly as it is in Ophioglossum. 

 In the adult leaves the upper part of the mesophyll is compact, but there is no 

 proper palisade tissue developed. Toward the lower surface the mesophyll becomes 

 looser. 



Until the plant has reached a considerable size the leaves remain undivided 

 and, except for the much greater size, closely resemble the early leaves of the young 

 sporophyte (see plate 1 1, fig. i). The simple leaves are succeeded later by trifoliate 

 ones, and finally five leaflets are developed. The long, fleshy petiole may reach a 

 diameter of a centimeter or more and a length of some 50 centimeters in large 

 specimens. The venation strikingly resembles that of a dicotyledonous leaf, the 

 pinnately arranged, secondary veins being connected by a plexus of small veins, 

 inclosing nearly square areoles within which a few free terminations are occasionally 

 found. The large pores upon the lower side of the leaf, formed by the greatly 

 enlarged stomata already referred to in the younger leaves, are plainly visible to the 

 naked eye, and sections of these look curiously like the pores upon the thallus of 

 certain Marchantiaceae (fig. 128). 



The stipules of the older leaves are very conspicuous and show much the same 

 structure as that noted for the earlier leaves. The young leaf is included within the 

 stipular sheath of the next older one, and near the apex the unbroken stipular sheath 

 of the youngest expanded leaf shows very plainly that the large stipules are joined 

 in front by a broad commissure, which extends entirely around the apex of the shoot, 

 exactly as it does in Helminthostachys, from which the sheath differs mainly in the 

 fact that it is divided above into the two stipules as it is in Botrychium virginianum, 

 and there seems no reason to doubt that we have to do with entirely homologous 

 structures (fig. 171, A). The stipules of the young leaves are covered with hairs 

 and scales similar to those noted in the young sporophyte. 



The roots arise from the ventral surface and flanks of the rhizome, and out- 

 number the leaves, to which they apparently bear no definite relation. 



The apical growth was not studied in the root of the older sporophyte, but it 

 is probable that in the large roots of the older plant the single apical cell found in 

 the early roots is replaced by a group of initials such as are found in the other 

 Marattiacea^, although it is barely possible that the single apical cell may be retained 

 here as it is in the ( )phiogIossacea?. Unfortunately, material was not available for 

 a study of this point. The roots in most cases are quite unbranched, as they are in 

 Euophioglossum. The only cases when branches were seen, were young sporophytes 

 in which the end of the root had been destroyed and two branches had arisen on 

 each side of the destroyed apex. This looks somewhat like a dichotomy and it is 

 barely possible that, as in Ophioglossum, there may be a real dichotomy of the root, 

 bur all of the cases that were found had much more the appearance of the formation 

 of two lateral roots. The young roots of the sporophyte are provided with multicel- 

 lular root hairs, like those of Daneea, but these disappear as the root becomes older. 



The central vascular cylinder of the root is surrounded by a circle of very large 

 mucilage ducts. The endodermis is clearly evident and the roots which I examined 



