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



55 



bundles, and the median one consisting of 1) a trio of bundles (the bundle-trio), 

 the middle bundle of which is compressed, with sieve tubes toward the sides, and the 

 others smaller or often wanting, and 2) a likewise compressed opposite bundle, the 

 xylem channel of which fuses with that of the main bundle of the trio. Between 

 the median and lateral areas and between the endodermis and the trio's main-bundle 

 and the opposite bundle there are important portions of mechanical cells. The whole 

 is surrounded by an 0— O-endodermis, the cells of which have three different degrees 

 of thickness. The strongest cells are situated outside the lateral bundle-groups, the 

 second strongest outside the median group. Other cells are thin-walled, combining cells 

 (fig. 19 G, z). In the ped- 

 uncle the cortical strands 

 are entirely lacking and the 

 vascular bundles are four, two 

 median and two lateral ones, 

 fig. 20, C. 



The anatomy of the leaf 

 presents on the upper surface 

 an epidermis of very large- 

 roomed cells, at short inter- 

 vals interrupted by narrow 

 ribbons of very small cells 

 (fig. 19, G), within which 

 more or less strong bund- 

 les of bast-cells are running. 

 All these strands make the 

 leaves many-nerved and f inely 

 striate. The vascular bund- 

 les are seven at the base of 

 the leaf, at the middle usu- 

 ally five. The marginal bast- 

 bundle is very strong. By 

 all that, the leaves grow very 

 durable and well able to endure unfavourable conditions. 



The tops of the branches are transformed into turios in the same way as in 

 P. zosterifolius and others, which endure the winter well and abundantly propagate 

 the species. 



Distribution. In the Swedish Museums specimens occur from N. America: 

 U. States, N. Angl. leg. E. Tuckerman (hb. Uppsal.); Massachusetts, leg. Morong 

 (hb. Stockholm.), Connecticut, leg. Morong (hb. Stockholm.), Minnesota, leg. Taylor 

 (hb. Stockholm.). No specimen from the Western States. Canada, Plevna, Ont. 02, 

 Fowler (hb. Stockholm.), Vancouver Isl., 87, Macoun (hb. Christian, et Haun.). 



Fig. 19. P. Robbinsii Oakes. A, Pistils, a, b, lateral view, c, stigma from 

 above, d, pistil from behind, ' T °; B, Anatomieal stem-diagram, str, subepidermal 

 strands, cs, cauline strands, \° ; C, Stele-diagram (more enlarged), ett; median op- 

 posite bundle, ti; bundle-trio, z, thinwalled endodermis cells; D, Epidermis of 

 the stem, longitudinal section, y : E, Transverse section of leaf (the one half), 

 in, niidiib, »', n", lateral nerves, skl, mechanical strands, ca. y°; F, Transverse 

 sect. middle part, of a leaf at the middle, more enlarged, ca. < y ) , «s, npper sur- 



face, Is, lower surface; G, Longitudinal section of the epidermis at F, 

 Longitudinal section of the epidermis of lower surface. 



//, 



