142 



J. O. HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOOETONS. 



the characteristics of the species: the coriaceous f loating leaves with petioles shorter 

 than the lamina and the compressed fruits (Koch), the obtuse, submersed leaves, 

 the obovate floating leaves with sloping base (Cham.). In our days the turios and 

 stem-anatomy (Raunkijer), the stigmas (Almquist) and styles (Hagström) have 

 been described more or less completely. 



The stem prolongs itself by branches of as far as the fifth rank. The ana- 

 tomy of the stem is constant whether the plant is growing in running or stagnant 



water. I have not been able to observe 

 any other change than a fusion or divi- 

 sion, within certain limits, of the cen- 

 tral cylinders vascular bundles. The 

 epidermis lacks a hypoderma and its 

 cells are large-roomed and stretched, 

 5 — 15 times the width. Bast-bundles 

 do not occur in the bark neither sub- 

 epidermally nor interlacunarly. The en- 

 dodermis always consists of O-cells and 

 the central stele has usually six lateral 

 and two median bundles, of which 

 the one is composed of three (a trio- 

 bundle). This trio-bundle sometimes 

 dissolves into a bundle-trio and some 

 one or other of the lateral bundles 

 often splits into two (see the f ig. Df). 

 The earlier authors (Camisso etc.) 

 were of the opinion that the species ty- 

 pically developed floating leaves and held 

 the form, endowed with such leaves as 

 main-form. This is also, no doubt, cor- 

 rect. Where the species aecidentally lacks 

 floating leaves, it depends on unfavour- 

 able external facts, as rapid streaming or 

 Bwelling of the water du ring the florifica- 

 tion. In sucli cases a leaf-form intermedi- 

 ate between submersed and floating leaves, is developed which I have called amphibial 

 leaves, a biologic occurrence by which the species adapts itself to the existing external 

 facts. Because of that it is more appropriate to rank the variations according to the 

 shape of the submersed leaves (CHAMJSSO, Hakt.man. FRIES etc.) than to the appear- 

 ance, presence or absence of the floating leaves (FlEBER and others). GHAMISSO sepa- 

 rates from the main-form a »forma angustijolia, qu» P.alpinusei annulatua Auet., folia 

 habet submersa summa 4 1 /* poll. Longa 5 lin. lata» etc. and a * forma latifolia quae P. 

 purpura8Cen8 SeIDEL, folia possidet submersa G 1 /- 1 poll. longa 15 lin. lata» etc. (Linnaa, 

 1827, 211—212). Thus the main-form becomes the commonest one with the submersed 



Fig. (13. /'. alpinus Balbis. A, Floating leaf, ,'. B, Pistils, a, 

 side-view b, from the inner side, J. C, Longitndinal section of the 

 iiini showing the embryo ("/. the potamen (endocar])) withitsthorn 

 (6) and the epiearp, e, f, D, Iransveree section of a central stele 



with more than sil lateral hnndles, Ir, eoinnound bandlei belonging to 



the Becond leal apwarda, '■/>■. opposite bundle, and fl>, feliar bnndle, 

 belonging to tho leaf next above \f. A.', Part of a transverse section 

 "i itu- Btem, ',''' '/'• epidermis, >''(./, endodermis, /, laonnar system, 

 /'. Top ol a yonng lignle, J, b /», chief ihm vis, ic, front-fleld, wg, 



wing-lii-M. 



