KUNGL. SV. VET. AKADBMIENS HANDLINGAE. BAND 55. N:0 5. 



43 



B 



is laminar in its character (of. the fig. 17), but no subepidermal, vaginal strands are 

 met with in this species which, thus, is less sclerenchymatous than the three next 

 in advance. The pseudo-hypodermal stratum is usually two-layered, very seldom enti- 

 rely lacking (fig. 16, H). 



The process of the outgrowth of the leaf-blade and its detaching from the 

 sheath is shown by the three drawings below of serial sections from a stem-leaf. A, is 

 a transverse section of the sheath at the middle, m, h — 6, vascular bundles (m = mid- 

 rib), str, bastbundles, I, lacunse. B, the same sheath, transv. sect, through the very 

 point of insertion of the lamina. The 

 dotted (+ + +) line represents the line of 

 demarcation between the lamina and the 

 ligule. The middle vascular bundle has 

 bent into the lamina, and, after forking, 

 the lateral bundle (6) to the left has sent 

 a branch into the leaf (n). The mecha- 

 nical bundles to the left have entered the 

 intercarinal part of the ligule. To the 

 right the process has not advanced so 

 far as on the opposite side. C, the pro- 

 cess is performed, lamina and ligule per- 

 fectly disjoined. All the mechanical strands 

 have entered the ligule save one which 

 has remained in its original place, but 

 will soon disappear in the leaf. No mar- 

 ginal strand is yet to be found. They 

 are formed a little later. Thus we have 

 found 1) that the middle bundle of the 

 sheath bends into the blade, 2) that each 

 of the lateral bundles (6 — h) gives off a 

 branch to the blade which forms the la- 

 teral vascular bundle (?i') of the leaves, 

 3) that the vaginal strands bend into the 

 ligule, but that one may occasionally con- 

 tinue into the lamina, where it, however, 



soon disappears (cf. fig. 16!), 4) that the ligule is at the base strongly two-ridged 

 with a vascular bundle in either ridge, 5) that the ligule is a so-called axillary ligule 

 according to the terminology of Colomb, and 6) that the faint marginal bast-bundle 

 of the leaf (Fig. 16, str) is laminar in its character. 



P. pectinatus is a somewhat more southern plant than P. filiformis. Its north 

 limit seems, over vast ranges of Europe and America, Japan and China, to coincide 

 with the year-isotherm of about + 1° (0°) C, but in Siberia the boundary line makes 

 a considerable curve, at least in the Yenesei-valley with high summer-warmth (at 

 the river-mouth as far as 20 — 21° C. : Scheutz), and the species is observed much 



Fig. 17. P. pectinatus L. The outgrowth of the blade and 

 it3 detaching from the sheath and tho origin of the axillary li- 

 gule. A, B, C, X 30. Explanation in the text above. D, Adult 

 ligule, J-, b—h, vascular bundles of ridges. 



