Wide Crown Research Articles

Tree allometry, leaf size and adult tree size in old-growth forests of western Oregon.

Relationships between tree height and crown dimensions and trunk diameter were determined for shade-tolerant species of old-growth forests of western Oregon. The study included both understory and overstory species, deciduous and evergreen angiosperms and evergreen conifers. A comparison of adult understory species with sapling overstory species of similar height showed greater crown width and trunk diameter in the former, whether the comparison is made among conifers or deciduous trees. Conifer saplings had wider crowns than deciduous saplings, but the crown widths of the two groups converged with increase in tree height. Conifer saplings had thicker trunks than deciduous saplings of similar crown width, possibly because of selection for resistance to stem bending under snow loads. The results suggest that understory species have morphologies that increase light interception and persistence in the understory, whereas overstory species allocate their biomass for efficient height growth, thereby attaining the high-light environment of the canopy. The greater crown widths and the additional strength requirements imposed by snow loads on conifer saplings result in less height growth per biomass increment in conifer saplings than in deciduous saplings. However, the convergence in crown width of the two groups at heights greater than 20 m, and the proportionately smaller effect of snow loads on large trees, may result in older conifers equalling or surpassing deciduous trees in biomass allocation to height growth.

THE PRIMARY THICKENING MERISTEM: DEFINITION AND FUNCTION IN MONOCOTYLEDONS

The PTM should be defined as a diffuse primary meristem which decreases in cross‐sectional extent (i.e., becomes a thinner‐walled cylinder) in a basipetal direction. It is associated with extensive anticlinal cell files and consists of cell initials that divide predominantly in periclinal planes. This meristem occurs typically in monocotyledons, especially those with thick, compact stems in species with rosette shoot axes. The PTM is also associated with a wide crown, so that the apical meristem is either slightly above the level of youngest leaf primordia, at approximately the same level as the leaf primordia, or distinctly sunken below surrounding stem tissue and the youngest leaf primordia. The location is dependent on the extent of primary thickening growth occurring in a particular species. A meristem associated with primary thickening of other plant groups should not be called a primary thickening meristem unless all of the above characteristics are shown to be associated with the meristem being examined. The primary thickening meristem is responsible for primary thickening of a stem axis. Its ontogenetic relationship with the STM needs further investigation. Extensive primary stem thickening has been observed in non‐monocotyledons (ferns, lycopods, cycads, and dictyledons). Some of these organisms appear to undergo primary thickening from a PTM in a similar process as that which occurs in monocotyledons. Further research is necessary to establish the mechanisms of primary thickening in these cases.

Factors Affecting Resistance of Field‐Planted Alfalfa Clones to the Alfalfa Weevil1

Seventy alfalfa, Medicago sativa L., clones representing a range of observed reactions to the alfalfa weevil, Hypera postica (Gyllenhal), were evaluated in a field test for oviposition and larval feeding, and for interrelationships between plant resistance and growth characteristics.Oviposition preference accounted for 26% of the variation among clones for larval feeding damage. Plants with decumbent growth, wide crown, little growth, and small stems tended to receive fewest eggs and suffer least larval feeding; they had many characteristics of Medicago falcata. Although weevils preferred to oviposit in plants with large stems, oviposition differences among clones were still significant after adjustment for stem size by covariance analysis. Weevils oviposited only sparingly in several of the clones with medium large stems. The following correlation coefficients were positive and significant: Number of egg masses and eggs per stem, stem diameter and eggs per stem, larval feeding and egg masses per stem, larval damage scores in different years, and number of egg masses in different years. Further study is needed to determine the kinds of resistance mechanisms involved and whether oviposition preference mechanisms reported here offer suitable control of alfalfa weevil damage.

THE PROJECTION PRAXINOSCOPE

M. GASTON TISSANDIER desciibes in La Nature an ingenious adaptation of the praxinoscope, under the above name, by means of which the images are projected on a screen, and are visible to a large assembly. Our engraving will give an idea of the arrangement and the effect produced. By a modification of the “lampascope,” M. Reynaud, the inventor, obtains by means of an ordinary lamp, at once the projection of the scene or background—by the object-glass which is seen at the side of the lantern—and of the subject, by another object-glass which is shown in front of and a little above the same lantern. For this, the positions or phases which form a is not visible in the figure; then a plane mirror inclined 45°, which reflects the rays and causes them to traverse the figures filling the openings of the crown. These rays, once more by the facets of the prism of mirrors, finally enter the object-glass, which transforms the vertical central image into a real image magnified on the screen. In making the two parts of the apparatus converge slightly, the animated subject is brought into the subject are drawn and coloured on glass, and are connected in a continuous band by means of any suitable material. One of these flexible bands is placed in the wide crown of the praxinoscope, which is pierced with openings corresponding to the phases of the subject. To understand the course of the luminous rays which go to form the image, it is necessary to bear in mind the condensing lens which, placed near the flame of the lamp, middle of the background, where it then appears to gambol. A hand-lever on the foot of the instrument allows a moderate and regular rotation to be communicated. This apparatus, with an ordinary moderator lamp, supplies well-lighted pictures and curious effects. It enables us to obtain, with the greatest ease, animated projections, without requiring any special source of light, by simply utilising the lamp in daily use.