Variant secondary growth in old stems of Ephedra campylopoda G. A. Mey

LEV-YADUN, S. & ALONI, R., 1993. Variant secondary growth in old stems of Ephedra campylopoda C. A. Mey. Ephedra campylopoda C. A. Mey is a woody climber of the Ephedraceae. The vascular rays of old, thick stems of E. campylopoda differ greatly from the known ray structure found in young stems of the same species, and from the common ray structure of other woody species. The large rays in thick stems include xylem in various orientations, and they intermingle with the axial system. We suggest that this is a variant secondary growth, a common characteristic of climbers.     

El Niño and tree growth near Jerusalem over the last 20 years

A strong correlation is observed between an El Niño index (anomalies in tropical Pacific sea surface temperature) and rainfall in the Judean foothills near Jerusalem over the past 20 years. These relationships clearly influenced the growth of local pine trees, as reflected in the width of their annual tree rings. The ability to predict El Niño events about a year in advance lend a special significance to relationships reported here for ecology, agriculture and water management in this climatic transition zone. To help explain the observed, long-range teleconnection we propose a possible mechanism based on a newly identified direct cloud connection between equatorial Africa (more directly affected by El Niño) and the Southeastern Mediterranean shoreland. The penetration and contribution of the moisture current from equatorial Africa to this region may depend on a shift in the usual rain generating moisture currents to southwesterly trajectories (passing over north Africa). The occurrence of such shifts is supported by the observed decrease in the mean ¹⁸O content of the local precipitation during El Nino winters.     

When may green plants be aposematic?

During the long, dry summers, the deserts of the Middle East are almost devoid of green plants. In the summer, most annuals, geophytes and hemicryptophytes either are dormant in the soil or have already been eaten by the grazing flocks. Many shrubs are summer deciduous or enter summer dormancy with minimal green canopy. However, there are several common plants that, contrary to the general phenology, are conspicuously green during summer, when all the surroundings are yellow. In such conditions, green is conspicuous and contrasts with the background, as do yellow, red and black in 'greener' ecosystems. The summer-green plants are also characterized by being poisonous or thorny as protection against herbivory. During winter and spring, when there are plenty of other green, more palatable annual plants, herbivory pressure is much lower and they need less protection. We propose that during summer in the dry desert, when most other plants are dry or indistinctive, a vivid green colour can be aposematic.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 413–416.     

Natural and Experimentally Induced Dispersion of Aggregate Rays in Shoots of Quercus ithaburensis Decne. and Q. calliprinos Webb

There are two types of sites where aggregate rays in Quercusithaburensis Decne. and Q. calliprinos Webb do not occur naturallyin the tree: branch junctions and small ridges of wood. Partialgirdling of Quercus trunks resulted in the dispersion of aggregaterays which diffused into numerous simple rays. The breakup ofaggregate rays following partial girdling is not a typical woundresponse since wounding is known to stimulate ray enlargement.The disaggregation of the huge rays reflects changes in therelationship between axial and radial signal flows. Aggregate rays, Quercus ithaburensis Decne., Quercus calliprinos Webb, ray differentiation, wood formation, xylem anatomy     

Fibres and Fibre-sclereids in Wild-typeArabidopsis thaliana

Examination of the fibre system in roots and shoots ofArabidopsisthaliana(L.) Heynh. revealed three types of fibres, distinguishedaccording to their site of differentiation: (1) short fibre-sclereidsin the secondary phloem of roots and shoots at the rosette level;(2) long fibres in the secondary xylem of the main root; and(3) very long fibres in the xylem of the inflorescence stems.These three types are in addition to the small number of primaryphloem fibres that are formed even in smallA. thalianaindividuals.These findings provide a basis for the use ofArabidopsis thalianaasa model system to study the processes leading to fibre differentiationin dicotyledons. Arabidopsis thaliana; differentiation; fibre-sclereids; inflorescences; phloem fibres; xylem     

Defensive ant,aphid and caterpillar mimicry in plants?

Here we describe three apparently novel types of visual insect mimicry in plants. In the first type, plants of Xanthium trumarium L. have dark spots and flecks that resemble ants (Formicidae) in size and shape in the epidermis of stems, branches and petioles, and plants of Arisarum vulgare Targ.-Tozz. have them on petioles and inflorescence stems. In the second type, the dark anthers of Paspalum paspaloides (Michaux) Scribner (= P. distichum ) are the size, shape and colour of aphids (Homoptera; Aphidoidea) and they sway in the wind like swivelling aphids. Similarly, the stems of Alcea setosa (Boiss.) Alef. are covered with dark flecks that look like aphids. Finally, immature pods of three wild annual legumes ( Lathyrus ochrus (L.) DC.; Pisum fulvum Sm.; Vicia peregrina L.) have conspicuous reddish spots, arranged along the pods, that appears to mimic lepidopteran caterpillars. In one of the species ( V . peregrina ) two different mimicking morphs were found. We propose that these morphological traits may serve as herbivore repellent cues and are part of the defence system of the plants.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 393–398.