Botanik (Subject) / Morphology (Lesson)

Morphologie = Lehre von der Struktur und Form der Organismen

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• Root metamorphosis: Aerial root -among others in epiphytes (plants growing on other plants) -there is a partly transformation of the rhizodermis into a multi-layered water-storing sponge tissue  e.g. Orchideen
• Root metamorphosis: Strangler roots -aerial roots that grow to the soil, densely surround a host tree and can kill the host (mostly some tropical figs)
• Life forms -the shoot and root organs can develop in a variety of ways -this is taken into account, for example, in the classification of life forms, which is based on the shape of the stem axis and, in particular, the position of the enduring organs (buds) phanerophytes, chamaephytes, hemicryptophytes, geophytes, helophytes, hydrophytes
• Leaf morphology -leaves are derived from the apical meristem and start as small bulges, the primordia -the lamina is the flattened part to absorb light -it is held at a distance from the branch by the petiole through which the veins pass from the stem -at the base of the petiole a pair of appendages, the stipules may be present -finally, the leaf base connects the petiole to the shoot
• Leaf morphology (1) -in compound leaves, the lamina is composed of individual leaflets -if they are pinnate, the leaflets sit along a rachis (which morphologically is the midrib) -in palmate leaves, the leflets originate from one point at the end of the petiole leaflets can again be compound by 2nd order leaflets
• Leaf morphology: parts of leaves -the parts of leaves are very variable -can also be missing -for instance, sessile leaves have no petiole and the lamina sits directly on the shoot -in some plant families, e.g. grass family and apiaceae (umbelliferae) the leaf base forms a leaf sheath around the shoot ->most of all, the lamina is very variable
• Leaf arrangement Arrangement on the leaves on the shoot is not random, but also follows genetically fixed rules -alternating leaf arrangement: only one leaf per node, the leaf on the next node exposed in different direction -opposite leaf arrangement: two leaves per node opposing each other, those on the next node usually displaced by 90 degree (decussate)   ->since branches grow from buds in leaf axils, the branching pattern follows the pattern of              leaf arrangement
• Leaf arrangement: whorled leaf arrangement -three or more leaves per node
• The length of internodes, petioles and leaf arrangement should optimize leaf functions -often, self shading is avoided -in case of a rosette (extremely shortened internodes) the self-shading is high, but lowest if the angle to the leaf on the next node is 137,5 degree (golden angle)
• The arrangement of alternating leaves follows rules, that can be explained mathematically -pinus sp. (pine) -Echinacea purpurea (purple coneflower): 34 and 55 spirals -Brassica aleracea convar: 13 and 21 spirals
• Leaf succession (Abfolge) Plants have a typical sequence of leaves -from the first leaves emerging from the seed, the cotyledons -to the leaves of a flower, which terminates the growth of a shoot
• Leaf succession: bracts (Deckblätter) ->more or less different from foliage leaves (Laubblätter), sometimes to support attraction of flowers e.g. Rhinanthus, Euporbia pulcherrima
• Leaf succession: Flowers -special developments of the plant stem with specialized leaves for sexual reproduction -flower formation ends shoot growth (no apical meristem is left) parts: carpel, stamen, petals, sepals
• Leaf succession: Buds -buds are shoots where the meristem is protected by leaves  -these are often specialized: bud scales
• Leaf anatomy -most leaves are foliage leaves (Laubblätter) for photosynthesis -leaves are composed of dermal tissue (epidermis), vascular tissue (the veins) and ground tissue (the mesophyll) Mesophyll: -composed of parenchyma, in typical dorsiventral leaves -pallisade parenchyma towards the upper  -spongy parenchyma towards the lower side
• Leaf anatomy: hypostomatic ->stomata on the lower side bifacial/dorsiventral e.g. Schneerose
• Leaf anatomy: epistomatic inverse bifacial / dorsiventral ->palisade parenchyma and stomata on the upper side, spongy parenchyma on the lower side e.g. Seelilie
• Leaf anatomy: equifacial ->palisade- or spongy parenchyma and stomata on all sides e.g. Mistel
• Leaf anatomy: unifacial ->the morphological upper surface of the leaf is missing, while the lover surface extends over the entire leaf - with palisade parenchyma and stomata e.g. Schnittlauch
• Leaf anatomy: venation -ferns and gymnosperms: veins seperate (often dichotomous) but do not merge -Angiosperms: veins diverge and merge   ->Dicots mostly reticulate   ->Monocots mostly parallell
• Anatomy -the vascular bundles in leaves continue through the petiole into the shoot, where they merge with the bundles in the shoot -when the leaves drop, they leave a distinct scar showing the disconnected bundles   ->the form of the scar is helpful for identification of plants during the leaf-less season
• Leaves: Gas exchange -Change in turgor through active import of K+ (together with anions) -Change in shape defined by orientation of cellulose fibrils and cell wall thickness ->osmotic uptake of water ->increase in turgor leads to increase in volume and change in shape Factors regulation whether the stomata is open or closed -light: stomata open for CO2 uptake (no need to lose water if CO2 cannot be used) -water saturation of the plant: danger of too much water loss (desiccation) ->stomata close -CO2-concentration inside the plant: low concentration -> open (to permit photosynthesis)
• Leaves: Gas exchange -Change in turgor through active import of K+ (together with anions) -Change in shape defined by orientation of cellulose fibrils and cell wall thickness ->osmotic uptake of water ->increase in turgor leads to increase in volume and change in shape Factors regulation whether the stomata is open or closed -light: stomata open for CO2 uptake (no need to lose water if CO2 cannot be used) -water saturation of the plant: danger of too much water loss (desiccation) ->stomata close -CO2-concentration inside the plant: low concentration -> open (to permit photosynthesis)

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