. Carnegie Institution of Washington publication. 80 THE OPHIOGLOSSALES rhe trace foi the second leaf, the Inst functional one, is usually provided with .1 single undivided bundle passing through rlu- petiole, hut sometimes this divides into two, as it does in the cotyledon of Botrychium virginianum. Where a single hunille occurs in the petiole it occupies a nearly nu-dian position and is concentric in structure, although the phloem is somewhat less developed upon the- adaxial side. I he xylem consists of a huge mass oftracheids surrounded by the phloem, which is reduced to about two rows of c
. Carnegie Institution of Washington publication. 80 THE OPHIOGLOSSALES rhe trace foi the second leaf, the Inst functional one, is usually provided with .1 single undivided bundle passing through rlu- petiole, hut sometimes this divides into two, as it does in the cotyledon of Botrychium virginianum. Where a single hunille occurs in the petiole it occupies a nearly nu-dian position and is concentric in structure, although the phloem is somewhat less developed upon the- adaxial side. I he xylem consists of a huge mass oftracheids surrounded by the phloem, which is reduced to about two rows of cells upon the adaxial side. Whethei the largest cells in this portion wen- sieve tubes was not determined. \\ lure two bundles are present they are somewhat smaller and are more nearly circular in outline than the single bundle, which they resemble in structure. In the ground tissue are large inter- cellular spaces which disappear at the hase of the leal, when- the ground tissue in cross-section appears almost solid. 1 his development of lacunas in the first foliage leaf recalls the similar ones in the cotyledons of Botrychium and Ophioglossum. In rhe older part of the rhizome there is a slight development of periderm on the dorsal side, which Farmer found to be the case also in the older rhizome. This periderm is restricted to the dorsal region and is obviousl) associated with the leaf bases, as it is in Botrychium and probably also in Ophioglossum. It presumably. I 54. Three sections f an oldei orophytc f Helminthostachys. 8. The stipulai sheath i- ab < i I From tin- third youngest leaf. acts as an absciss layer, such as [effrey demonstrated in Botrychium, and this not only causes tin- separation of tin- old leaves hut perhaps also acts as .1 protective layei to the hat scais. I he absence of periderm from tin ventral side is no doubt connected with the strictly dorsal position of the leaves. I he latei loots, like the first one, grow from a single apica
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Keywords: ., bookauthorcarnegie, bookcentury1900, bookdecade1910, bookyear1911
