. La biologie d'eau douce. Biologie des eaux douces. L'ENSEMBLE DE LA VÉGÉTATION AQUATIQUE i8s des plantes les supporter ont été adaptés à la vie sur terre ou au moins vécu sous l'exposition à une perte d'eau par transpiration. D'autres ouvertures dans la feuille ont également été trouvés chez certaines espèces. Ces derniers se produisent à l'apex de la feuille plus fréquemment dans les feuilles submergées que dans la flotte. L'ouverture ne montre pas de structure particulière, comme c'est le cas des stomates, et il est formé par la désintégration et l'apostasie du tissu à l'apex, de sorte que les vaisseaux conducteurs dans les nervures de la feuille sont exposés à, et en lien direct

• Contributeur: The Book Worm / Alamy Banque D'Images
• ID de l’image: RDA6NR
• Taille du fichier: 7,1 MB (269,3 KB Téléchargement compressé)
• Autorisations: Modèle - non | Propriété - non
• Dimensions: 2083 x 1199 px | 35,3 x 20,3 cm | 13,9 x 8 inches | 150dpi

Informations supplémentaires

Cette image appartient au domaine public, ce qui signifie que le droit d’auteur a expiré ou que le titulaire du droit d’auteur a renoncé à ses droits. Les frais facturés par Alamy couvrent l’accès à la copie haute résolution de l’image.

Cette image peut avoir des imperfections car il s’agit d’une image historique ou de reportage.

. Fresh-water biology. Freshwater biology. THE LARGER AQUATIC VEGETATION i8S of the plants bearing them were adapted to life on land or at least lived under exposure to loss of water by transpiration. Other openings in the leaf have also been found in some species. These occur at the apex of the leaf more frequently in the submerged leaves than in the floating ones. The opening does not show any special structure, as is true of stomata, and is formed by the decay and falling away of the tissue at the apex, so that the conductive vessels in the veins of the leaf become exposed to, and in direct communi- cation with, the water. In some cases this disin- f^o. 260. zanmchdua ' repens. Submerged tegration of tissue at the apex may go so far as to !fj^' '^'x^'ibout'™' change to a marked degree the shape of the apex, '^"" sauvageau.) making it rounded instead of pointed (Figs. 261 and 262). The formation of the opening seems to occur before the leaf matures but is seldom found on the young leaves. In addition to the species already known as bearing these openings the writer may mention that of Vallisneria spiralis on whose half- grown leaves he has observed them. Some authors have suggested that the passage of water through the conduc- tive tissue is facilitated and that the excretion is aided. This is really a supposition and has never been proved. The presence of an earthy coating on the leaves and stems of some water plants may be commonly ob- served. This mineral incnistation appears like a coating of mud on the leaf in many cases, while in others it is not so conspicuous and is only noticeable when the plant is handled. Only the submerged organs seem to bear the incrustation, even the lower surface of floating leaves being less favor- able to its formation and much less fre- quently bearing it. Potamogeton pectinatus is seldom, . Fig. 261. Zostera nana. Apical portion of a mature submerged leaf, showing the change of form at the apex due to decay of apical

Recherche dans la banque de photos par tags

• bookcentury1900
• bookdecade1910
• booksubjectfreshwa
• bookyear1918