KUNGL. SV. VET. AKADEMrENS HANDLINGAR. BAND 55. N:0 5. 



35 







Oq., 



str 



OCT, 





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tween these chief lateral nerves and the border at equal distance from both appear 

 in broad or middle-sized leaves small secondary nerves (vascular bundles), the leaves 

 thus becoming five-nerved (fig. 12, E, n^). These faint nerves, however, can scarcely 

 be perceived with the usual magnifying glass, and the leaves therefore look three- 

 nerved. The space between the primary lateral nerve and the margin presents a 

 light appearance on account of the interjacent marginal lacunae, see the fig. ! Be- 

 tween the midrib and chief lateral nerves in the upper and lower surface, occur sub- 

 epidermally 1 — 4 bast-bundles (fig. 12, E, str.) and occasionally a subepidermal 

 strand in the very border with another also farther in (fig. 12, E*). Such mecha- 

 nical strands, however, are never te be found between the chief lateral nerve {n^) 

 and the secondary ones {n^), even in the broadest leaves. In the ordinary »3- 

 nerved» leaves of P. pectinatus the primary lateral nerve runs much nearer to the 

 margin and the secondary nerve or bast-bundle (fig. 16, D, str.) almost subepider- 

 mally at a distance of 2 — 3 cell- A 

 layers from the marginal epidermis, 

 wherefore it cannot be perceived 

 at all by a usual magnifying glass. 

 On close examination these two spe- 

 cies can easily be distinguished from 

 each other by the leaf-structure. On 

 the other hand the leaves exhibit 

 closer anatomical relations to P. 

 subretusus and recurvatus than to 

 P. pectinatus. 



Another essential characteristic 

 in the anatomy is the above men- 

 tioned short cubic epidermis-cells 

 (fig. 12, D), of great importance 

 especially in studying the hybrids. 

 The epidermis-cells of the peduncle 

 are somewhat more elongated, about 

 three times as long as broad. The epidemis-cells of the stem, on the other hand, 

 are constantly short even in the most streched internodes. Through this anatomical 

 structure the stem obtains a most considerable strength. 



An examination of the anatomy of the turios proves that in them all the 

 cauline arrangements for mechanical purposes are totally absent: 1) Epidermis-cells 

 considerably longer; 2) The cortex is without the regular square channels and their 

 bast-bundles. Only the vascular bundles are left. 3) Bark-cells very thin-walled 

 and cylindric, not square-formed, with tapering ends and with wider or narrower 

 interspaces corresponding to the stem-lacune. 4) Endoderm-cells not at all or but 

 slightly thickened, and 5) the pith deprived of mechanical elements. 



The species does not vary much. A slender form is by TiSELius named f. 

 tenuior. 



o\ 



Fig. 12. P. vaginatus Tukcz. A, B, Transverse section of the cen- 

 tral stele, lower part of the stem, from two different individnals showing 

 the form and the arrangement of the bundles (hatched parts) and xylem- 

 channels (A'), eight-bundled diagrams, ca. \^. C, Stele-diagram of the pedun- 

 cle, showing the same parts as in A and B, ^/. D, Epidermis of the stem, 

 longitudinal and tangential section, \^. E, Transverse section of a stem - 

 leaf, middle part, showing the position of the five nerves of the figure 

 11, A (hatched), the small subepidermal strands (str) and the lacunar 

 system (/.); * signifies the places for rarely appearing strands, n}, n^ late- 

 ral nerves, V. 



