Distorted leaves

Surface Reconstructions in W. In earlier sections, we have noted that the pair functional formalism is not always appropriate as the basis for an energetic description of metals. One case where this is evident is in the context of the surface reconstructions seen on certain bcc transition metals. In particular, the (001) surface of both W and Mo exhibits fascinating reconstructions, and as in the case of the Au(OOl) surface, the symmetry breaking distortions leave few vestiges of their crystallographic ancestry. 

In order to accommodate smaller ions, such as nickel(II), the porphyrin skeleton may contract by ruffling, with little loss of aromaticity like a pleated skirt the pyrrole rings rotate alternately clockwise and counterclockwise about their respective M-Np vectors. This distortion leaves the four porphyrinato nitrogen atoms, Np, still coplanar. Alternatively, the porphyrin skeleton may buckle to give a saddle conformation the Np atoms may acquire a small tetrahedral distortion in this process. M-Np bonds as short as 1.92 A have been observed. Metals with one or two electrons in their 3d ,2- 2 orbital have a radius larger than 2.00 A. In order to accommodate them in the plane of the porphyrin, the porphyrin skeleton expands. M-Np separations as long as 2.07 A may occur with the metal still centered in the plane of the Np atoms. 

In the smectic A phase the director is always perpendicular to the plane of the smectic layers. Thus, only the splay distortion leaves the interlayer distance unchanged [7], and only the elastic modulus K i is finite while K22 and Kzz diverge when approaching the smectic A phase from the nematic phase. On the other hand, the compressibility of the layered structure and the corresponding elastic modulus B is taken into account when discussing the elastic properties of smectic phases. The free energy density for the smectic A phase, subjected to the action of an external electric field, is... 

Distorted leaves. Aphids and capsids feeding on crop leaves can cause the crop leaves to become distorted. 

A snap can be characterized by the geometry of its spring component. The most common snaps are the cantilever type, the hollow-cylinder type (as in the lids of pill bottles) and the distortion type (Fig. 4-15). These snaps include those in any shape that is deformed or deflected to pass over interference. The shapes of the mating parts in a hollow cylinder snap is the same, but the shapes of the mating parts in a distortion snap are different, by definition. These classifications are rather nominal, because the cantilever category is used loosely to include any leaf-spring components, and the cylinder type is used also to include noncircular section tubes. 

Signs The first symptoms consist of darker green streaks in a pattern of "dots" and "dashes" ("Morse code" streaking) on the lower portion of the midrib. Later, the streaks appear on the secondary veins of the leaf and then on the leaf blade. Suckers that develop after infection are usually severely stunted, which causes the leaves at the top of the stem to become bunched. Leaves are usually short, stiff, erect, and more narrow than normal. Severely infected banana plants usually will not fruit. If the plant does bear fruit, it will likely be distorted and twisted. 

Peach leaf curl disease infects leaves as they unfold in spring, causing red blistering and distortion of the foliage. A temporary shelter to keep rain off until all the leaves have appeared should reduce infection. 

The organisms Pyricularia oryzae, which causes rice blast, and Helminthosporium oryzae, which causes brown leaf spot, can be controlled with complexes of the ligands 1-phenyl-3-methyl-4-nitroso-2-pyrazolin-5-one (36) and 3-methyl-4-nitroso-2-pyrazolin-5-one (37). The complexes were of the type ML Xj (L = 36, 37 X = C1-, Br, N03 ) or [ML2]Y2 (Y = C104 ). The former were assigned an octahedral or distorted octahedral structure and the latter are tetrahedral. The most active nickel complex was (38).92... 

Fluorides are readily translocated to the tip and margin of leaves in the transpiration stream. If atmospheric levels of HF are low enough, the intercostal injury will not develop, and the fluoride concentration will increase at the periphery of the leaf. Acute fluoride intoxication at the margin of dicotyledonous plants, according to Solberg et al. (18), is first characterized by a collapse of the spongy mesophyll and lower epidermis, followed by distortion and disruption of the chloroplasts of the palisade cells, and finally, distortion and collapse of the upper epidermis. The injured area soon turns brown during hot, dry weather, but this symptom may be delayed if the weather is cool and damp. 

Typically, PAN attacks spongy mesophyll tissue surrounding the substomatal chambers on the lower side of the leaf. When tissue immediately beneath the lower epidermis is killed, the epidermis dries, producing a glazed or bronzed appearance on the lower leaf surface. Usually there is no evidence of injury on the upper surface when the glazed or bronze symptom develops. Later, as the upper part of the leaf continues to grow, it cups downward, becomes rugose, and distorted. 

The sunflower budworm or bud moth (Suleima helianthana Riley), considered a minor pest of the sunflower in which damage is sporadic, also feeds on the Jerusalem artichoke (Pedraza-Martinez, 1990 Rogers, 1979). In North America, the insect is found from Maryland to California and south to Mexico. Damage is caused by larval feeding, typically on the apical bud or axils of upper leaves, producing distorted, misshapen plants. Young larvae act as leaf miners or enter a leaf rib, while older larvae enter and feed on buds, leaf axils, stems, and bracts. 

Leaves distorted, orange-yellow spots on leaf undersides. Cause Rust. This fungus produces orange pustules, distorting the leaves and making branch tips swell. Rust usually doesn t harm the tree much, except for detracting from the appearance. Clean up and destroy fallen leaves and branches in autumn. To prevent the spread of mild infections, spray leaves with sulfur early in the season. 

If leaf tips are distorted or brown, and leaves are stippled with white, look for onion thrips. Heavy infestations cause plants to wither and turn brown. Adults are tiny, slender, yellow to brown, rapidly moving, winged insects. The larvae can barely be seen with the naked eye. Thrips thrive in hot, dryvjveather. Trap them with sticky traps hung st above plant level. Try blue, yellow, and white traps to see which work best. Treat plants with insecticidal soap or a commercial pyrethrin spray or dust to control severe infestations. 

Leaves covered with white powder. Cause Powdery mildew. Powdery white or grayish fungal patches grow on upper leaf surfaces of plants subject to poor air circulation or hot, humid weather. As the disease spreads, leaves become distorted and ma drop off. Powdery mildew is more severe when growing conditions are unsatisfactory. 

Leaves distorted, orange-yellow spots on leaf undersides. Cause Rust. See "Leaves distorted, orange-yellow spots on leaf undersides on page 99. 

Insect pests such as yucca plant bugs anc scales are more prevalent and likely to cause damage where yuccas are native. Aphids ma> infest Adam s-needle see Leaves, stems, and buds distorted, sticky clusters of small insects on page 177 for controls. Fungal leaf spot may appear and are best controlled with cu tural practices Limit excess water on foliagr and remove severely infected plant parts. 

Comparative leaf histological responses — Lesion development in fronds of P. aquilinum and leaves of P. vulgaris and H. annuus was very similar. In these three species initial injury was characterized by collapse of one to six cells on the adaxial epidermis. Normal turgid cells which comprised a continuous epidermis became flaccid witL an initial increase in cellular stain intensity. This tissue collapse resulted in a depression on the leaf surface. Underlying mesophyll tissues showed little or no distortion at this stage. 

Within cross-sections of Tradescantia there is a regular distribution of both trilaminar epidermal complexes and vascular bundles within the leaf mesophyll. The leaf mesophyll consists of parenchyma cells which are uniform in size and shape. Initial exposure to simulated acid rain of pH 2,7 resulted in the collapse of outer epidermal cells in some areas. Distortion of underlying epidermal cells in the trilaminar sites and disruption of upper mesophyll cells also occurred. The next stage of lesion development varied slightly among lesions. In most lesions, collapse of mesophyll cells near the adaxial epidermis was evident. However, cell hypertrophy was also observed in about 50% of all lesions. Hypertrophic cells attained a cell volume three times that of unaffected cells. Supportive cells near vascular bundles were usually partially collapsed at this stage. 

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