From falling to flying: the path to powered flight of a robotic samara nano air vehicle

This paper details the development of a nano-scale (>15 cm) robotic samara, or winged seed. The design of prototypes inspired by naturally occurring geometries is presented along with a detailed experimental process which elucidates similarities between mechanical and robotic samara flight dynamics. The helical trajectories of a samara in flight were observed to differ in-flight path and descent velocity. The body roll and pitch angular rates for the differing trajectories were observed to be coupled to variations in wing pitch, and thus provide a means of control. Inspired by the flight modalities of the bio-inspired samaras, a robotic device has been created that mimics the autorotative capability of the samara, whilst providing the ability to hover, climb and translate. A high-speed camera-based motion capture system is used to observe the flight dynamics of the mechanical and robotic samara. Similarities in the flight dynamics are compared and discussed as it relates to the design of the robotic samara.     

Intraspecific variation in samara morphology and flight behavior in acer saccharinum (Aceraceae)

We studied intraspecific variation in samara morphology and flight behavior within and among parent trees of Acer saccharinum (silver maple), with a particular focus on the effect of samara shape. Samara mass, area, wing loading, and descent rate from a 4.5-m indoor balcony were measured for 50 undamaged mature samaras from each of six parents. We found significant differences among parental types for all morphological variables and descent rate. These differences yielded a 50% range in mean dispersal potential among the six parents. There was a strong linear correlation between descent rate and square root of wing loading when mean values were plotted for each of the six parental types. But there was considerable within-parent variation for all measured variables, including substantial nonallometric variation in wing loading caused in part by poor correlations between wing area and fruit weight. Parents also differed widely in the relationship between square root of wing loading and descent rate (linear r² = 0.150-0.788), with one parental type showing no significant relationship. Fruits from the same parent with similar values of the square root of wing loading showed as much as a 75-100% difference in descent rate. The usefulness of mass : area indices such as wing loading is limited by its exclusion of aerodynamically important factors such as mass distribution and wing shape, which in our case caused the six parents to behave aerodynamically almost as if they were six separate species.     

被子植物翅果的多样性及演化

翅果能够依靠风力进行传播, 可能是被子植物快速散布和物种分化的一个重要因素。狭义的翅果是指果皮延伸成翅且不开裂的干果; 广义的翅果则包括果皮、花被片或苞片形成果翅的所有果实。根据果翅形态及其生长方式的不同, 广义的翅果可分为单侧翅果、周位翅果(圆翅果与蝶翅果)、棱翅果、披针翅果、翼状萼翅果、叶状苞翅果6种类型, 其空中运动方式有自旋式(单侧翅果、翼状萼翅果)、波浪式(周位翅果、叶状苞翅果)、翻滚自旋式(周位翅果)、直升机式(披针翅果、翼状萼翅果)和滚筒式(棱翅果)。棱翅果与圆翅果在被子植物基部类群樟目就有发生, 并同时出现在单子叶植物和双子叶植物中, 可能是最早出现的翅果类型。翅果的演化过程呈现出果翅数量增加、果翅偏向单侧和果翅负荷(果实质量与果翅面积之比)降低的趋势, 以利于适应较小的风并增加传播距离。果翅除了促进果实与种子的风力传播外, 还具有物理防御、调节种子萌发和促进二次传播等作用。泛热带分布的金虎尾科有着极其丰富的翅果类型, 与其多次跨洋长距离扩散密切相关, 可以作为研究翅果适应与演化的一个模式类群。结合生态和演化-发育生物学方法, 研究不同类型翅果在适应风力传播方面的差异、萼片或苞片发育成翅的分子与遗传机制、翅果不同类型的演化历史及其对被子植物物种多样性的影响等是今后值得探讨的重要问题。     

Diversity and evolution of samara in angiosperm

翅果能够依靠风力进行传播, 可能是被子植物快速散布和物种分化的一个重要因素。狭义的翅果是指果皮延伸成翅且不开裂的干果; 广义的翅果则包括果皮、花被片或苞片形成果翅的所有果实。根据果翅形态及其生长方式的不同, 广义的翅果可分为单侧翅果、周位翅果(圆翅果与蝶翅果)、棱翅果、披针翅果、翼状萼翅果、叶状苞翅果6种类型, 其空中运动方式有自旋式(单侧翅果、翼状萼翅果)、波浪式(周位翅果、叶状苞翅果)、翻滚自旋式(周位翅果)、直升机式(披针翅果、翼状萼翅果)和滚筒式(棱翅果)。棱翅果与圆翅果在被子植物基部类群樟目就有发生, 并同时出现在单子叶植物和双子叶植物中, 可能是最早出现的翅果类型。翅果的演化过程呈现出果翅数量增加、果翅偏向单侧和果翅负荷(果实质量与果翅面积之比)降低的趋势, 以利于适应较小的风并增加传播距离。果翅除了促进果实与种子的风力传播外, 还具有物理防御、调节种子萌发和促进二次传播等作用。泛热带分布的金虎尾科有着极其丰富的翅果类型, 与其多次跨洋长距离扩散密切相关, 可以作为研究翅果适应与演化的一个模式类群。结合生态和演化-发育生物学方法, 研究不同类型翅果在适应风力传播方面的差异、萼片或苞片发育成翅的分子与遗传机制、翅果不同类型的演化历史及其对被子植物物种多样性的影响等是今后值得探讨的重要问题。     

AUTOROTATION, SELF-STABILITY, AND STRUCTURE OF SINGLE-WINGED FRUITS AND SEEDS (SAMARAS) WITH COMPARATIVE REMARKS ON ANIMAL FLIGHT

• 1 A samara is a winged fruit or seed that autorotates when falling, thereby reducing the sinking speed of the diaspore and increasing the distance it may be transported by winds. Samaras have evolved independently in a large number of plants.
• 2 Aerodynamical, mechanical, and structural properties crucial for the inherent self-stability are analysed, and formulae for calculation of performance data are given.
• 3 The momentum theorem is applied to samaras to calculate induced air velocities. As a basis for blade element analysis, and for directional stability analysis, various velocity components are put together into resultant relative air velocities normal to the blade's span axis for a samara in vertical autorotation and also in autorotation with side-slip.
• 4 When falling, a samara is free to move in any sense, but in autorotation it possesses static and dynamic stability. Mainly qualitative aspects on static stability are pre sented. Simple experiments on flat plates at Reynolds numbers about 2000 as in samaras, showed that pitch stability prevails when the C. M. (centre of mass) is located 27–35 % of the chord behind the leading edge. The aerodynamic c.p. (centre of pressure) moves forward upon a decrease of the angle of attack, backward upon an increase. In samara blades the c.m. lies ca. one-third chord behind the leading edge, and hence the aerodynamic and centrifugal forces interact so as to give pitch stability, involving stability of the angles of attack and gliding angles.
• 5 Photographs show that the centre of rotation of the samara approximately coincides with its c.m.
• 6 The coning angle (blade angle to tip path plane) taken up by the samara is determined by opposing moments set up by the centrifugal and aerodynamic forces. It is essentially the centrifugal moment (being a tangent function of the coning angle, which is small) that changes upon a change of coning angle, until the centrifugal and aerodynamic moments cancel out at the equilibrium coning angle.
• 7 Directional stability is maintained by keeping the tip path plane horizontal whereby a vertical descent path relative to the ambient air is maintained. Tilting of the tip path plane results in side-slip. Side-slip leads to an increased relative air speed at the blade when advancing, a reduced speed when retreating. The correspondingly fluctuating aerodynamic force and the gyroscopic action of the samara lead to restoring moments that bring the tip path plane back to the horizontal.
• 8 Entrance into autorotation is due to interaction between aerodynamic forces, the force of gravity, and inertial forces (when the blade accelerates towards a trailing position behind the c.m. of the samara).
• 9 The mass distribution must be such that the c.m. lies 0–30 % of the span from one end. In Acer and Plcea samaras the C.M. lies 10–20% from one end, thereby making the disk area swept by the blade large and the sinking speed low.
• 10 The blade plan-form is discussed in relation to aerodynamics. The width is largest far out on the blade where the relative air velocities are large. The large width of the blade contributes to a high Re number and thus probably to a better L/D (lift/drag) ratio and a slower descent.
• 11 The concentration of vascular bundles at the leading edge of the blade and the tapering of the blade thickness towards the trailing edge are essential for a proper chord wise mass distribution.
• 12 Data are given for samaras of Acer and Plcea, and calculations of performance are made by means of the formulae given in the paper. Some figures for an Acer samara are: sinking speed 0.9 m/sec, tip path inclination 15°, average total force coefficient 1.7 (which is discussed), and a L/D ratio of the blade approximately 3.
• 13 The performances of samaras are compared with those of insects, birds, bats, a flat plate, and a parachute. They show the samara to be a relatively very efficient structure in braking the sinking speed of the diaspore.
• 14 In samaras the mass, aerodynamic, and torsion axes coincide, whereas in insect wings the torsicn axis often lies ahead of the other two. Location of the torsion axis in front of the aerodynamic axis in insects tends towards passive wing twisting and passive adjustment of the angles of attack relative to the incident air stream, the direction of which varies along the wing because of wing flapping.
• 15 Location of the mass axis behind the torsion axis may lead to unfavourable

     

Seed size and dispersal potential of Acer rubrum (Aceraceae) samaras produced by populations in early and late successional environments

In order to determine if red maple dispersal potential or seed size change during secondary succession, samaras were collected from five populations located in early successional environments and five populations located in late successional environments. Wing loading ratios (samara mass—mg/samara area—cm²), which are inversely proportional to dispersal ability, were computed for all samaras, and seeds were excised from each samara and weighed. Samaras from the early successional red maples showed slightly but significantly lower wing loading ratios than those from the late successional environments. This result corresponds with the conclusions reached by several theoretical investigations of seed dispersal evolution that predict that recently founded populations will show greater dispersal abilities than more established populations. The earlier successional populations had slightly heavier seeds than the later successional populations, which suggests that the changes in community composition and dynamics that occur during this successional sequence do not select for heavier seeds in older red maple populations. Coefficients of variation for wing loading and seed size showed no consistent trends with successional stage, which indicates that variation in these characters does not decrease as succession proceeds.     

长白山9种槭树的翅果扩散及种子萌发研究

翅果的风媒传播是槭属植物的主要扩散方式之一,且与种子萌发有着密切关联,但具体机理一直还并不明确。以分布于长白山的9种槭树为对象,探讨翅果的形态特征,测定它们在空气中的垂直沉降速度、不同风速下的水平扩散距离以及在扩散距离上的种子萌发率,进而比较并分析翅果的形态性状与沉降速度、水平扩散距离的相关性以及萌发率在不同扩散距离上的差异性。结果表明：(1) 9种槭树的翅果长、宽和面积与沉降速度、水平扩散距离均呈负相关;尽管如此,翅果形态并不是风传播物种的最佳分类指标,而翅载力能较好地反应物种的风传播能力;(2)翅果垂直沉降速度和水平扩散距离间存在显著负相关,表明沉降速度越小,翅果在空气中停留的时间越长,水平方向上扩散距离越远,且强风有助于提高翅果的扩散能力;(3)沉降速度最慢的花楷槭在不同风速下的水平扩散距离均最远,而沉降速度最快的拧筋槭水平扩散距离最短;(4)种子萌发率随扩散距离的增加呈下降趋势。上述结果不仅为深入理解翅果的风力传播机制以及种子萌发对水平扩散距离的响应机制提供科学依据,还可为种群实生更新方面的理论研究提供参考。     

The effect of samara wing presence on predation of Acer pseudoplatanus (Sapindaceae) seeds on the ground

The key selective pressure shaping the morphology of samaras is seen as enhancing primary wind-borne dispersal from the parent plant to the ground. However, the consequences of the samara wing of primarily wind-dispersed tree species for post-dispersal processes has not been well studied. We explored whether the presence of this wing in Acer pseudoplatanus either deters or promotes predation after dispersal, either by increasing the time and energy required to predate the seed or by increasing the seed's visibility to predators. We found that wing-removed fruits were preferred, suggesting that the presence of samaras makes seed handling more expensive for granivores. Further, we found that fewer seeds were consumed from treatments that contained the most winged seeds, thus there was no evidence of the samaras making seed finding easier for granivores. We conclude that the presence of the wing may offer an anti-predatory benefit as well as aiding primary dispersal.     

Gone with the wind and the stream: Dispersal in the invasive species Ailanthus altissima

Dispersal is a key process in plant invasions and is strongly related to diaspore morphology. Often, dispersal comprises more than one step, and morphologies adapted to a primary dispersal mechanism can aid or detract from a secondary one. The aim of this work was to assess the relationship between primary wind dispersal and secondary water dispersal in Ailanthus altissima, an invasive tree species. Wind and water dispersal potential and their association with the morphological characteristics of samaras were assessed under controlled conditions to ensure the repeatability of the measurements. We found a direct positive relationship between primary wind and secondary water dispersal in A. altissima. The main morphological characteristics of the samara that affected the success of the two types of dispersal were side perimeter and mass. However, a possibility of dispersal specialisation exists, as one morphological characteristic (samara width) affects wind dispersal negatively but water dispersal positively, and dispersal potential and samara morphology have been shown to differ across individuals.     

Fossil Ptelea samaras (Rutaceae) in North America

Fossil samaras referred to the extant rutaceous genus Ptelea L. comprise an artificial collection of five distinct taxa with convergent fruit morphologies. Critical reexamination of these fossils revealed that only one of the five samara types can be referred to Ptelea. Two of the forms can be assigned without reservation to Tiliaceae (Pteleaecarpum = Craigia) or Caprifoliaceae (“Ptelea” cassioides [part], “Ptelea” miocenica [part]). Taxonomic affinities of the two remaining fruit types (“Ptelea“ eocenica, “Ptelea“ cassioides [part]) are undetermined. Genuine fossil Ptelea samaras are restricted to Miocene floras in the western United States, including the Hog Creek (Weiser) and Succor Creek floras near the Oregon–Idaho border and the Stinking Water flora of east-central Oregon. These samaras bear the names P. miocenica Berry and P. enervosa H. V. Smith. The holotype of P. miocenica is a caprifoliaceous infructescence similar to that of Dipelta Maximowicz, so P. enervosa, previously considered a synonym of P. miocenica, is the valid combination for fossil Ptelea samaras. P. enervosa samaras are the oldest reliably determined fossil Ptelea fruits. These samaras indicate that the Toddalieae-Pteleinae lineage of subfamily Toddalioideae has been present in North America since the Miocene, rather than the Eocene as suggested by previously misidentified specimens.     

Secondary dispersal mechanisms of winged seeds: a review

Winged seeds, or samaras, are believed to promote the long‐distance dispersal and invasive potential of wind‐dispersed trees, but the full dispersive potential of these seeds has not been well characterised. Previous research on the ecology of winged seeds has largely focussed on the initial abscission and primary dispersal of the samara, despite it being known that the primary wind dispersal of samaras is often over short distances, with only rare escapes to longer distance dispersal. Secondary dispersal, or the movement of the seeds from the initial dispersal area to the site of germination, has been largely ignored despite offering a likely important mechanism for the dispersal of samaras to microhabitats suitable for establishment. Herein, we synthesise what is known on the predation and secondary dispersal of winged seeds by multiple dispersive vectors, highlighting gaps in knowledge and offering suggestions for future research. Both hydrochory and zoochory offer the chance for samaroid seeds to disperse over longer distances than anemochory alone, but the effects of the wing structure on these dispersal mechanisms have not been well characterised. Furthermore, although some studies have investigated secondary dispersal in samaroid species, such studies are scarce and only rarely track seeds from source to seedling. Future research must be directed to studying the secondary dispersal of samaras by various vectors, in order to elucidate fully the invasive and colonisation potential of samaroid trees.     

The fossil record of Eucommia (Eucommiaceae) in North America

Reproductive and vegetative remains of Eucommia from 25 localities in the United States, Canada, and Mexico document the wide distribution of this genus in North America during the Cenozoic. Autofluorescent elastic latex filaments bearing capitate termini are preserved in nearly all of the remains and provide conclusive evidence of their affinity to Eucommia. Four species of Eucommia are recognized on the basis of the characteristic samaras: E. eocenica from middle Eocene strata of the Mississippi Embayment in Missouri, Tennessee and Mississippi; E. montana from early Eocene to early Oligocene localities in British Columbia, Washington, Oregon, Utah, Colorado, and Montana; E. constans from Neogene rocks in central Mexico; and E. jeffersonensis n. sp. from the latest Eocene or earliest Oligocene John Day Formation of Oregon. Atypical specimens of E. montana and E. eocenica are the first records of two-seeded fruits for the genus. Eucommia leaves from Eocene localities in British Columbia and Mississippi are the first records of Eucommia foliage in North America whose identifications are confirmed by the presence of capitate latex strands. These leaves and a specimen from Oregon are referred to E. rolandii n. sp. Fruit evolution in Eucommia may have involved increases in samara size and symmetry, and reduction in seed number from two to one, perhaps as adaptations for wind dispersal. All fossil Eucommia samaras from North America are smaller and less symmetrical than those of the living species, E. ulmoides. Preliminary flight tests of E. ulmoides samaras and of models of the fossils suggest that E. ulmoides fruits are aerodynamically better suited for wind dispersal than the fossils.     

Parvileguminophyllum coloradensis, a new combination for Mimosites coloradensis Knowlton, Green River Formation of Utah and Colorado

The purported ash samara, Fraxinus flexifolia (Lesquereux) Brown (1940) from the middle Eocene Green River Formation, is shown to be the same as small inequilateral legume leaflets identified as Mimosites coloradensis Knowlton. Because the name Mimosites Bowerbank is restricted to legume pods with mimosoid affinities, the new combination Parvileguminophyllum coloradensis (Knowlton) Call and Dilcher is proposed for the previously supposed samara, here recognized as a leaflet, and for leaflets currently placed in M. coloradensis. A lectotype is designated from among Knowlton's original specimens. The transfer of Brown's so-called Fraxinus samara to Parvileguminophyllum coloradensis (Knowlton) Call and Dilcher comb. nov. removes Fraxinus fruits from the list of macrofossil remains presently recognized in the Green River flora. The distribution of Fraxinus samaras in Paleogene assemblages from North America is briefly discussed. The paper concludes with a discussion of nomenclatural problems that may arise when two or more fossil organ types are united under a common name. We argue that this practice should be avoided except when the organs are found in organic connection, or when other indisputable evidence of their conspecificity is preserved, such as shared anatomical or biochemical features. By itself, the co-occurrence of disassociated fossil organs at different localities is only circumstantial evidence of their conspecificity.     

Chemical Composition and Phytotoxic Effects of Essential Oils Obtained from Ailanthus altissima (Mill.) Swingle Cultivated in Tunisia

Ailanthus altissima Mill. Swingle (Simaroubaceae), also known as tree of heaven, is used in the Chinese traditional medicine as a bitter aromatic drug for the treatment of colds and gastric diseases. In Tunisia, Ailanthus altissima is an exotic tree, which was introduced many years ago and used particularly as a street ornamental tree. Here, the essential oils of different plant parts of this tree, viz., roots, stems, leaves, flowers, and samaras (ripe fruits), were obtained by hydrodistillation. In total, 69 compounds, representing 91.0–97.2% of the whole oil composition, were identified in these oils by GC‐FID and GC/MS analyses. The root essential oil was clearly distinguishable for its high content in aldehydes (hexadecanal ( 1 ); 22.6%), while those obtained from flowers and leaves were dominated by oxygenated sesquiterpenes (74.8 and 42.1%, resp.), with caryophyllene oxide ( 4 ) as the major component (42.5 and 22.7%, resp.). The samara oil was rich in the apocarotenoid derivative hexahydrofarnesyl acetone ( 6 ; 58.0%), and the oil obtained from stems was characterized by sesquiterpene hydrocarbons (54.1%), mainly β‐caryophyllene (18.9%). Principal component and hierarchical cluster analyses separated the five essential oils into four groups, each characterized by the major oil constituents. Contact tests showed that the germination of lettuce seeds was totally inhibited by all the essential oils except of the samara oil at a dose of 1 mg/ml. The flower oil also showed a significant phytotoxic effect against lettuce germination at 0.04 and 0.4 mg/ml (?55.0±3.5 and ?85.0±0.7%, resp.). Moreover, the root and shoot elongation was even more affected by the oils than germination. The inhibitory effect of the shoot and root elongation varied from ?9.8 to ?100% and from ?38.6 to ?100%, respectively. Total inhibition of the elongation (?100%) at 1 mg/ml was detected for all the oils, with the exception of the samara oil (?74.7 and ?75.1% for roots and shoots, resp.).     

STUDY OF THE VERTICAL AUTOROTATION OF A SINGLEWINGED SAMARA

1. Autorotation of a single-winged samara is a highly nonlinear phenomenon that represents a delicate equilibrium between gravity, inertia and aerodynamic effects. Therefore, in order to analyse this phenomenon, an accurate detailed model is necessary. Such a model has not been presented in the past. Recently the authors derived a detailed model which is briefly described in the paper. 2. The aerodynamic contributions present the most complicated part of the phenomenon. These contributions are treated using the blade-element/momentuin method, with certain improvements and additions. These improvements are necessary due to inherent differences between samara wings and other rotary wing systems (aircraft propellers, helicopter rotors, etc.). 3. The cross-sectional aerodynamics of the samara is characterized by relatively small Reynolds numbers, high angles of attack and rough surfaces. While these characteristics are different from other rotary wings, they are typical of the wing cross-sections of insects and birds. Therefore the lift and drag coefficients, which are necessary for the analysis, are obtained using available data for insect and bird wings. 4. The results of the theoretical model are compared with experimental results of tlvo kinds. The first kind includes results for a samara of an Acer platanoides that were reported in the literature. In addition, a special experimental model of a samiira was built and tested. This model offers a simple way of varying the configuration in order to study (experimentally) the effect of different geometric parameters on the autorotation. 5. In the light of the uncertainty in the aerodynamic coefficients, it can be concluded that there is quite a good agreement between the theoretical and experimental results. Thus, after LTalidation, the theoretical model is used for a parametric study to find the influence of different parameters on the autorotation. The important results of this study are outlined below. 6. The spanwise flolv component and the tangential component of the induced velocity have a very small influence and thus can be neglected. 7. It is important to include in the analysis the effects of the axial induced velocity, the tip effect, and the drag of the root region. 8. Since chordwise variations of the centre of pressure location, as a function of the angle of attack, were seen in the past (based on over simplified analyses) as the mechanism which is responsible for the samara stability, this effect is also added to the model. While the influence of this effect on the pitch angle is large and small on the sinking rate, it results in an increase in the deviation between the theoretical and experimental results. 9. Autorotation is sensitive to the cross-sectional aerodynamic coefficients. This sensitivity is critical since the available data on these coefficients is, to say the least, unsatisfactory and require significant improvement.     

云南金钱槭果实、种子形态分化研究

对5个云南金钱槭(Dipteronia dyeriana Henry)天然居群的果实、种子形态进行研究.测量了果实和种子的长度、宽度、重量等12个表型性状指标.数据统计结果显示5个云南金钱槭居群按果实、种子大小进行排序为蒙自(MZ)>屏边(PB)>文山1(WSh1)>文山3(WSh3)>文山2(WSh2).表型性状在居群内和居群间均存在着一定程度的变异,其中居群间变异系数的平均值从0.064(果实整体形态,PL/PB)到0.197(种子重量,SW),相比之下果实整体形态最为稳定.居群间形态总体差异显著性配对t检验结果说明,多数居群间已产生较明显的形态分化.Ward聚类和相关分析结果都表明表型性状与生态因子、海拔高度之间存在着一定程度的相关性,多种生态因子的共同作用是导致果实、种子形态特征产生差异的主要原因.     

Responses of photosystem II of white elm to UV-B radiation monitored by OJIP fluorescence transients

Photosystem II (PSII) activities in both samara and leaf of white elm (Ulmus pumila L.) were significantly inhibited by enhanced UV-B radiation (UVBR). UVBR disturbed both the donor and acceptor sides of PSII. The plastoquinone (PQ) pool size on the acceptor side, the trapped excited energy for complete reduction of Q_A, and the proportion of closed PSII reaction centers (RCs) increased, with PSII RCs being transformed into dissipative sinks for excitation energy under UVBR. However, samara and leaf responded to UVBR in different ways. A decrease in the F ₀ for leaf induced by UV-B radiation suggests the formation of fluorescence-quenching centers. An increase in the V_I for leaf under UVBR might mean the accumulation of reduced Q_A and PQ. F ₀ and V_I for samara showed opposite change pattern. Leaf has the mechanism of regulation of the amount of light reaching the RC through decreasing the number of light-harvesting chlorophyll molecules under UVBR while samara may be unable to regulate the light-harvesting capacity. PSII in samara was more susceptible to UVBR than that in leaf, with PI_ABS for samara decreasing more rapidly by a factor of 6.4 than that for leaf. Samara can recover more easily from UVBR-induced damage to PSII than the leaf.     

榆属（榆科）一新种——绵竹榆

绵竹榆的花秋季开放,翅果柱头面被毛,其两侧的翅较果核为窄,果核位于翅果上端接近缺口处,与榔榆(Ulmus parvifolia Jacq.)相似,但树皮深灰色,不规则鳞块状浅裂,叶片先端渐尖,花被片裂至基部,宿存,边缘上部生纤毛,翅果狭椭圆形,中部最宽,向两端渐变窄,果梗与花被等长,长约2 mm,果序梗长约1 mm,而明显不同。     

Rate of cocoon production by the larva of the fly Rhynchosciara americana and storage sites of precursors

A chemical analysis of Rhynchosciara americana cocoons at four stages of spinning was performed and the amount and rate of the cocoon production was measured. These results, together with the amount and distribution of the nutrient reserves in the larva during spinning, were used to identify the possible storage sites of cocoon precursors. The physiology, mechanics, and regulation of spinning by R. americana are discussed.     

绒毛白蜡二态型果实的扩散特征

多态型果实或种子的出现对植物种群的扩散具有重要的意义。绒毛白蜡(Fraxinus velutina)的果实具有二态型特征,主要表现在果翅数量上不同,分别定义为二翅型和三翅型果实,为了比较两类果实在风传扩散时的差异,研究了两类果实的形态、果翅结构和扩散距离及扩散时长。在大型封闭地下室内,以电扇在不同速度档位产生的气流作为风源,分别从2、1.5、1m处手动释放果实,对风速为0、4.6、6.5、7.3m/s时的果实扩散距离及扩散时长进行了比较;并在此基础上对果实的形态特征与扩散特征进行了线性相关分析。结果表明:在同一高度及相同风速下,三翅型果实的水平扩散距离都极显著的大于二翅型,但其相应的扩散时长都小于二翅型。在相同情况下,三翅型的果实沉降速度显著高于二翅型。两类果实随着释放高度的增加,其扩散距离和扩散时长都相应的增加;随着风速的升高,其扩散距离及扩散时长都相应的增加。三翅型果实质量显著高于二翅型,相反,三翅型果翅长与宽都显著小于二翅型。两种翅型的果翅细胞结构都一样,细胞内部都呈现气囊状,果翅表面沿纵轴方向有流线型的纵棱。通过直线相关分析发现,翅型是对扩散距离和扩散时长影响最显著的形态特征;与果实释放高度相比,风速是影响绒毛白蜡果实扩散距离与扩散时长最显著的环境因素。绒毛白蜡三翅型果实比二翅型果实传播的远,关键在于其具有三翅,三翅对阵风瞬间响应,使得沉降速度较二翅型高,可以在瞬时风的作用下,快速传播到较远的距离。三翅型与二翅型在扩散方式上的结合增强了绒毛白蜡的生存与定殖机会。