20 STRUCTURE AND LIFE-HISTORY OF HAY-SCENTED FERN. 



phloems present no differences. The inner pericycle is one to two, rarely 

 three, cells thick. Inner endodermis is like the outer in cross-sections, but 

 seems to have longer cells (see table, p. 19). 



The layer of starchy medulla inside the vascular ring- corresponds with 

 that on the outside. In a rhizome with six to eight layers outside, there are 

 about seven inside. In another with three or four (mostly three) layers 

 outside, there are two or three (mostly three) inside. But the inner cells 

 are smaller than the outer (see table, p. 19). The inner sclerenchyma 

 cells (sclerotic medulla) are longer and narrower than the outer, and have 

 thicker and blacker walls (figs. 63, 64, 76, 77, 80). They form a core 

 from twelve to twenty-two cells in diameter. 



The above type of stem is called by Gwynne-Vaughan (1901) a solenostele 

 (adj. solenostelic) and by Jeffrey (1897) an amphiphloic siphonostele. The 

 description may serve as a definition of these terms. 



At the node (figs. 3, 4, 66) the cylindrical leaf -base springs from the 

 slightly larger stem at a right or acute angle, usually without altering the 

 size or shape of the stem. Occasionally the stem is slightly enlarged 

 below the node, and rarely there is a slightly prominent ridge between leaf 

 and stem, as at a fork. 



The leaf -trace or vascular bundle of the leaf (petiolar meristele) leaves 

 the stem as a trough-like band (horseshoe-shaped in transverse section) 

 which is of the same thickness as the wall of the vascular tube of the stem 

 (fig. 82) . The concavity of the trough faces obliquely upward and forward 

 in most leaves. But where the leaf-insertion is ventral (figs. 83-87) or 

 lateral the trace faces directly tipward. When the insertion is dorsal the 

 trace faces directly forward. At the place where the leaf -trace leaves the 

 tubular vascular system of the stem a distinct leaf- gap occurs (fig. 82). 

 This is a narrow slit in the stem bundle, through which the medullary and 

 cortical tissues become continuous. The gaps differ in shape and in their 

 exact relation to the leaf -trace. One gap is 11 mm. long and 1.2 mm. 

 wide, with acute ends, and with the leaf -trace attached near the middle of 

 the ventral side. Another is 14 mm. by 1 mm. A third is 1.8 mm. by 

 0.3 mm., rounded at both ends, with the leaf -trace occupying nearly all of 

 one side. The average size (of ten) is 5.45 mm. long and 0.53 mm. wide. 

 Usually the anterior end is rounded and the posterior end tapering and 

 acute, with the leaf -trace attached along one side, at or near the anterior 

 end. Such a gap is figured by Gwynne-Vaughan (1903, plate 33, fig. l). 

 When the leaf-insertion is dorsal the trace arises symmetrically from the 

 rounded posterior end of the gap. Lateral leaf -traces differ scarcely at all 

 in their origin from the usual dorso-lateral type. Ventral leaves, spring- 

 ing from a fork, are symmetrically attached to each arm of the stem (figs. 

 83-87 ) . The trace lies like a trough with its concavity upward . Approach- 

 ing such a nodal fork along the main stem, the stele first becomes wide 

 and flat. Then a slit is found on the upper side, and as the branches 



