. Critical researches on the potamogetons. 140 J. O. HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOGETONS. with shorter lamina. Submersed leaves usually 5—7-nerved with tapering base and top, generally 3—5 mm broad, with a lacunar portion filling, in the lower half of the leaf, the whole space between the midrib and the chief lateral nerves, by which the species shows affinity to the Euhybridi and Java- nici. Pollen spheric and small-grained. Stem com- pressed in the proportion of 2:1, and sometimes slightly furrowed. The epidermis is destitute of a hy- poderma, but instead of this its cells are
. Critical researches on the potamogetons. 140 J. O. HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOGETONS. with shorter lamina. Submersed leaves usually 5—7-nerved with tapering base and top, generally 3—5 mm broad, with a lacunar portion filling, in the lower half of the leaf, the whole space between the midrib and the chief lateral nerves, by which the species shows affinity to the Euhybridi and Java- nici. Pollen spheric and small-grained. Stem com- pressed in the proportion of 2:1, and sometimes slightly furrowed. The epidermis is destitute of a hy- poderma, but instead of this its cells are very short, often cubic or 1,5—2 times as long as the width. This is a significant and excellent characteristic of this spe- cies, especially of great importance for determining its hybrids. The cortical bast- and vascular bundles appear only laterally in the utmost interlacunar wall (see the fig!) as in P. Robbinsii, and sometimes with one or another bundle so near to the epidermis that it might almost be called subepidermal. Proper subepi- dermal bast absent. Endodermis of 0-cells. The cen- tral cylinder has two median bundles, one compound and one simple, and three lateral on either side, all separated from one another by mechanical tissue. This anatomical diagram of the trio-type is very constant in this species. The submersed leaves are destitute of sclerenchymatous tissue in the lacunar part but possess a strong bast-bundle in either margin. The species does not vary much, chiefly to the size only. Var. portoricensis Graebner does not belong to this species (see below!). Var. cayugensis Wi'egand is a nearly allied distinct species. P. Nuttallii and P. cayugensis certainly occupy a separate position within the subsection, but they never- theless stand in the nearest affinity to its other species. This especially becomes clear from the style, consisting of submersed leaves, showing the form and Quly in a Swelling ou the ovary, the fruit-form, and nervation, slightly e
Size: 1013px × 2467px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiod, bookdecade1910, bookyear1916
