摘要:

The geometry of plant axis flexure is analyzed as the result of orthotropic growth and the stresses caused by a vertical weight distribution along the axis. Distal responses to light and gravity and proximal sagging flexure result in a curvilinear axial geometry. The stresses associated with this geometry are analyzed by means of the flexure theory for curved beams. A flexed plant axis is shown to conform to some portion of a logarithmic spiral, r = r0ekθ, of which a special case is circular flexure, k 0. Calculations of the maximum bending moment, Mmaxand the maximum tensile stress,max, acting parallel to the axis indicate that the optimal mode of flexure (one that minimizes Mmaxandmax) is some arc of a circle. Examination of 11 plant taxa indicates that this mode of curvature is statistically the most prevalent condition in plants lacking or having limited secondary growth. Indeterminate apical growth of orthotropic axes is shown to result in a type of failure where portions of vertical axes are reapportioned into a horizontal or supported position.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13385.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

The vascular system of the leaf ofAmaranthus retroflexusL. was examined quantitatively, and plasmolytic studies were carried out on it to determine the solute concentration in cells of the phloem at various locations in the leaf. The proportion of phloem occupied by sieve tubes varies considerably with vein size and leaf size. Collectively, the cross‐sectional area of sieve tubes of all tributaries at their points of entry into either a secondary or midvein far exceeds the total cross‐sectional area of sieve tubes at the bases of those major veins. In addition, the total volume of sieve tubes in the “catchment area” of a secondary vein is much greater than total sieve‐tube volume of the secondary vein itself. The plasmolytic studies revealed the presence of positive concentration gradients in the sieve tubes of the lamina from the minor veins and tips of the secondaries to the bases of the secondaries and from the tip to the base of the midvein. The C50(the estimated mannitol concentration plasmolyzing, on the average, 50% of the sieve‐tube members) was 1.5 m for minor veins and tips of secondary veins and 1.1 m for the bases of secondaries; 1.3 m for the tip of the midvein and 0.6‐0.7 m for the midvein in the basal third of the lamina.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13386.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Floral development inPiperwas compared between four‐staminate species (P. aduncumandP. marginatum) and six‐staminate species (P. amalago). AllPiperspecies have a syncarpous gynoecium composed of three or four carpels. The floral apex is initiated by a periclinal division in the subsurface layer in the axil of a bract 40‐55 μm high; initiation of the bracts occurs separately and considerably earlier. The floral primordium widens and the first pair of stamens are initiated at either side. The median anterior stamen forms next, and the median posterior later. This sequence is common to all species studied. In the six‐staminateP. amalago, the last two stamens form simultaneously in lateral‐anterior positions. The stamens hence arise as pairs, and symmetry is bilateral or dorsiventral. The three or four carpels arise simultaneously; they are soon elevated on a gynoecial ring by growth of the receptacle below the level of attachment of the carpels to produce a syncarpous gynoecium. The floral apex lastly produces the solitary basal ovule and is used up in its formation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13387.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Newly matured prickly sida (Sida spinosa) seeds were hard, but afterripening, heat or pressure permitted water entry solely via a predefined region of the chalazal area. In this region, the raising of a “blister” formed by separation of the palisade of the seed coat from underlying tissues preceeded measurable water uptake by prickly sida seeds. A single subpalisade layer, unique to the region beneath the blister, was involved in the sequence of events in seed water uptake. The lateral walls of subpalisade cells invariably broke near the palisade border and cell contents were extruded onto the surface. This report describes the cytological development of the subpalisade layer from 1‐21 days post anthesis. Cells beneath the potential “blister” near the chalazal slit developed into columnar subpalisades and cells beneath the subpalisades or beyond the margins of the potential blister, developed into oval, thick‐walled chalazal cap cells. By 6‐10 days, distinct features of the subpalisades included: 1) thin portions in lateral walls due to lack of secondary wall depositions at the palisade border; 2) progressive accumulation of fibrous material in numerous vacuoles; and 3) progressive coalescence of osmiophilic bodies and degeneration of cytoplasmic contents. At 21 days, the seeds were dehydrated, mature and hard, but the thin, lateral subpalisade walls were still intact and had not broken. The thin‐walled portions were predetermined weak sites that break, permit palisade separation, expose the area under the blister to available moisture and result in subsequent imbibition of water by the seed. The hydrophilic, fibrous material extruded from the ruptured subpalisade cells may attract water to the newly exposed surface and facilitate penetration of water into the nutritive and embryonic seed tissues.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13388.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Observations have been made on the pollination ecology ofCabomba carolinianaGray in Texas. Flowers are trimerous with morphologically similar perianth parts. The adaxial corolla spurs are nectariferous and attract small Diptera (e.g.Notiphila cressoniandHydrellia bilobifera). Anthesis occurs for 2 consecutive days with flowers opening about 10:00 a.m. and closing around 4 p.m. on each day. First‐day flowers have short, indehiscent stamens and longer pollen‐receptive stigmata which arch outward over the nectaries. In 2nd‐day flowers the stamens have elongated to the level of the stigmata and extrorse dehiscense occurs above the nectaries. Stigmata of 2nd‐day flowers are pressed together at the center of the flower and are nonreceptive to pollen. Insects attracted to 2nd‐day flowers in search of nectar become dusted with pollen (due to the position and extrorse dehiscence of the anthers) and as insects fly to 1st‐day flowers, achieve cross‐pollination by virtue of the stigmata position over the nectaries. Seed anatomy is similar to that of other nymphaeaceous genera (i.e., abundant perisperm, little cellular endosperm, a haustorial nucellar “tube,” and a small dicotyledonous embryo). Pollination morphology and comparative xylem anatomy support the segregation ofCabombafrom the Nymphaeaceae, sensu stricto. The anatomical correlations between seeds and the myophilous pollination syndrome (found elsewhere in Nymphaeaceae, sensu lato), however, suggest a phyletic relationship.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13389.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Extra‐floral nectaries of nine species ofPassiflorawere studied with light and electron microscopy prior to and during secretion. There is no evidence of ER or Golgi participation in the secretion of nectar. The vascular tissue supplying the nectary is characterized by companion and phloem parenchyma cells which are usually larger than the sieve elements, a configuration similar to that found in leaf minor veins. In the petiolar nectaries, large masses of membrane‐bound protein are commonly found in these cells. This protein is absent in laminar nectaries.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13390.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Patterns of capsule development and methods of seed dispersal are described and compared for 16 neotropical species ofDalechampia.In 15 species all the capsules in a single inflorescence develop simultaneously. In one species,D. spathulata, the capsules develop sequentially. I suggest that the difference betweenD. spathulataand the other species is the result of the fact thatD. spathulataoccurs in a low‐light, rainforest environment, whereas the other species grow in high‐light environments. Sequential development of capsules appears to reduce the loss of seeds to seed predators in species that occur in light‐limited environments. The seeds of all 16 species ofDalechampiaare dispersed by explosive dehiscence of the capsules. Within the genus there are several different adaptations that increase the average dispersal distance for the seed crop.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13391.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

An embryogenic suspension culture was established from cultured inflorescence segments ofPennisetum americanumin Murashige and Skoog's medium supplemented with 2.5 mg/1 2,4‐dichlorophenoxyacetic acid (2,4‐D) and 5% coconut milk. The suspension was composed of two major cell types: 1) small, richly cytoplasmic and starch‐containing cells, generally found in small, compact clumps, here termed embryogenic cells; and 2) elongated, thick‐walled cells with large vacuoles. By manipulating the duration of culture and dilution ratios (cell suspension: fresh medium) at the time of subculture, suspensions consisting predominantly of embryogenic cells were obtained. Suspensions grown for 2‐3 wks were transferred to agar media with reduced amounts of 2,4‐D. This resulted in the production of hundreds of globular and early cotyledonary embryoids. Further development of the embryoids was promoted by their transfer to a medium containing abscisic acid. Many of the embryoids germinated and produced normal green plants. Atypical embryoids, some containing many shoot meristems and a leafy scutellum, were also observed. The relevance of such atypical embryoids in the interpretation of organogenesis and embryogenesis reported in tissue cultures of cereal species is discussed. It is also suggested that somatic embryogenesis occurs in tissue cultures of most, if not all, species of cereals and grasses.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13392.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

A low relief, green turf‐forming alga of a heterotrichous habit was discovered in the coral reef microcosm, Museum of Natural History, Smithsonian Institution. Erect filaments bore lateral, specialized sporangia and together with basal filaments possessed septal plugs between adjacent cells, grossly similar to the “pit connections” of red algae.Data are presented which: 1) establish the identity of our plant with a plant recently described asPilinia earleaeGallagheretHumm from the Florida Gulf coast; 2) support our establishment of the new genusSmithsoniellaand our transfer ofP. earleaeto this new taxon.Additional data on pigmentation and cytology are related to the fine structure of other selected green algae to develop and test three hypotheses, viz.Smithsoniella earleaerepresents either: 1) a symbiotic association between a green and a red alga; 2) an alga which belongs to either theUlotrichales, Chaetophoralesor theChroolepidales; or 3) an alga representing an evolutionary link between filamentous forms of the Ulvophyceae and members of the coenocytic siphonalean complex (e.g., Codiales or Caulerpales) of the Chlorophyta. Data refute hypotheses 1 and 2 but do lend support to the third hypothesis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13393.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Terminal vertical cladodes (flattened stems) ofOpuntia ficus‐indicagrowing in widely separated locations were nonrandomly oriented. On plantations at 33°S latitude in Chile individual cladodes tended to orient in the same direction as the planted cladodes on which they developed. However, after 2 years unshaded new cladodes tended to face east‐west. Terminal cladodes also tended to face east‐west for irrigatedO. ficus‐indicain California (at 34°N) and in Israel (32 to 33°N), but cladodes developing in the winter tended to face north‐south. Except for the residual effect of initial planting direction, the observed patterns tended to maximize the interception of photosynthetically active radiation (PAR). Specifically, east‐west cladode orientation would maximize PAR interception, except for cladodes developing near the winter solstice at latitudes more than 27° from the equator. Nocturnal acidity increases and hence productivity would generally be light‐limited, since the nocturnal increase in acidity was 90% saturated for a total daytime PAR of 24 mol m–2day–1and the PAR received on vertical surfaces is usually less than this. Topographical features can modify the orientation patterns, since at a site where PAR was considerably blocked by surrounding mountains the maximal nocturnal acidity increases and peak in cladode orientation occurred 20° from facing east–west. Laboratory studies showed that developing cladodes oriented toward a horizontal light and were rotated an average of 16° in a direction that increased PAR interception compared to the cladodes on which they developed. Such phototropic responses, the higher productivity of favorably oriented cladodes, and the tendency to orient similarly to the underlying cladode presumably accounts for the overall orientation patterns observed, where up to four times more cladodes may face in a particular direction than at right angles to it.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13394.x

出版商:Wiley    

年代:1982

数据来源: WILEY