. Critical researches on the potamogetons. 86 J. O. HAGSTEOM, CRITICAL RESEARCHES ON THE POTAMOGETONS, the pitch of all the small- and narrow-leaved species, so the P. confervoides goes to the contrary extremity by developing no mechanical tissue or exceptionally a single subepidermal strand or so. On the other hand the development of such a tissue in the central cylinder is very lively, by which at all events the stem grows both very strong and flexible. A one-layered pseudo-hypoderma covering the epidermis inside also contributes to strengthen the stem. Most similar species instead of this s
. Critical researches on the potamogetons. 86 J. O. HAGSTEOM, CRITICAL RESEARCHES ON THE POTAMOGETONS, the pitch of all the small- and narrow-leaved species, so the P. confervoides goes to the contrary extremity by developing no mechanical tissue or exceptionally a single subepidermal strand or so. On the other hand the development of such a tissue in the central cylinder is very lively, by which at all events the stem grows both very strong and flexible. A one-layered pseudo-hypoderma covering the epidermis inside also contributes to strengthen the stem. Most similar species instead of this stratum are furnished with a complete circle of subepidermal bast-bundles. But in P. ochreatus, as we have seen, both these reinforcements occur combined also. The central cylinder, surrounded with a strong 0-endoder- mis, has the bundles arranged in the usual three groups, here often separated by bast-cells and by ligni- fied or for mechanical purposes trans- formed pith-cells. The median bundles are two with common xylem cavity. The lateral ones are two or only one on either side (oblong diagram). In the floral axis the median bundles run near to each other, their xylem parts dissolve, forming a common channel with great lumen and their bast-sheaths unite into a common endodermis-like sheath, out- side which the two lateral bundles are placed one on either side (fig. 34, B). A one-celled pseudo-hypo- derma is also to be found here. Both the stem and the peduncle have a rounded crosscut-form, and although elongate like that of a Colegeton- species, the latter, however, is stiff as usual. The fig. 34, G, shows the ana- tomy of the leaf. In the middle of the leaf there runs a vascular bundle with its bast-sheath, round which a circle of small lacunae is arranged. On both sides there appears a row of ample lacunae and in the borders sometimes a row of narrow channels, and always a little bast-bundle. One or a few subepidermal bast-bundles in the middle part strengthen the leaf-str
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Keywords: ., bookcentury1900, bookcollectionbiod, bookdecade1910, bookyear1916
