The circadian movement of the lamina of primary leaves of Phaseolus coccineus L. is mediated by antagonistic changes in the length of the extensor and flexor cells of the laminar pulvinus. The cortex of the pulvinus is a concentric structure composed of hexagonal disc-like cells, arranged in longitudinal rows around the central stele. Observations with polarization optics indicate that the cellulose microfibrils are oriented in a hoop-like fashion in the longitudinal walls of the motor cells. This micellation is the structural basis of the anisotropic properties of the cells: tangential sections of the extensor and flexor placed in hypotonic mannitol solutions showed changes only in length. As a consequence a linear correlation between length and volume was found in these sections. Based on the relationship between the water potential (which is changed by different concentrations of mannitol) and the relative volume of the sections and on the osmotic pressure at 50% incipient plasmolysis, osmotic diagrams were constructed for extensor and flexor tissues (cut during night position of the pulvinus). The bulk moduli of extensibility, [Formula: see text], were estimated from these diagrams. Under physiological conditions the [Formula: see text] values were rather low (in extensor tissue below 10 bar, in flexor tissue between 10 to 15 bar), indicating a high extensibility of the longitudinal walls of the motor cells. They are strongly dependent on the turgor pressure at the limits of the physiological pressure range.In well-watered plants, the water potentials of the extensor and flexor tissues were surprisingly low,-12 bar and-8 bar, respectively. This means that the cells in situ are by no means fully turgid. On the contrary, the cell volume in situ is similar to the volume at the point of incipient plasmolysis: the cell volumes of extensor and flexor cells in situ were only 1.01 times and 1.1 times larger, respectively, than at the point of incipient plasmolysis, whereas at full turgidity (cells in water) the corresponding factors were 1.8 and 1.5. It is suggested that the high elasticity of the longitudinal walls, the anisotropy of the cell walls, and the low water potential of the sections which is correlated with slightly stretched cell walls in situ, are favourable and effective for converting osmotic work in changes in length of the pulvinus cells, and thus for the up and down movement of the leaf.
The roots ol" leafy spurge {Euphorbia estda L.) iiornially produce shool bud.s abundanily nrar the soil surlace but with decreasing rrequency at increasing depths. By placing fragincnls ol roots collected from various depths in the soil in shallow flat.s in a glasshouse, it was dfmon.stratctl that root fragments from all depths down to 2-8 m do not differ appreciably in regenerative capacity and this capacity is not dependent upon the presence of preformed shoot buds. By collecting mot fragineiit.s from the same stand throughout ihe growing season it was shown that reg;:nerativc capacity is lowest in June at the time of niaximum flowering. The implications of these findings are discussed in relation to the control of diis species.Sur la riginhaiion des fragments de racines de Euphorbia esula L.Resume. Les racines de Euphorbia esuta L. produisent normalement des l>ourgeons, aboiidamment pres de la surface de la terre, mais plus rarcment a mesure que la profondeur augmente. Kn met taut des fragmentsderacinesrccueillisa diverses profondeurs dans des lerrines en serre, il apparait que les fragments de toutes les profondeurs jusqu'a 2,8 m De varient pas d'une maniere significative dans leur capacitt? de rt'gen^ralion, et que cette tapacii^ ne di^pciid pas de la presence de bourgeons d^jil d^veloppcs. En rassembiant les fragments de racines d'une meme provenance au cours de toute la saison de croissance, il apparait cjue la capacity de r^g^n^ration est minimum au mois de juin, alors que la (loraison est au maximum. IJJ sigtiitication de ces d^couvertes est di^ it regard du desherbage de cette espece. (Jber die Regetieration von Wurzttfragmenteti mn Euphorbia esula L. Zusanumenrassung. IJie Wurzeln von Euphorbia esula erzeugen normalerweise besonders nalie der Bodenobrrfliiche Sprossknospcii, deren Haufigkeit mit zunehmender Tiefe abnimmt. Durch Pflanzen von VVurzelfragmenten aus verschiedenen Tiefen in Pikierkasten wurde gezeigt, dass Wurzelfragmentr von alien Tiefen bis zu 2,8 111 keine wescntlichen Unterschiedr in ihrer regcnerativeii Fahigkeil aufweisen und dass diese Fiihigkrit nicht von vorhergi hildeten .SprossknosiK-n abhangt. Das .Sammcln von Wurzelfragmenten vom gleichen Bestand wahrend einer Wachstumsperiode zeigte, dass die regenerative Fahigkeit wahrend dcs Hohepunktes dcr Bliitezeit im Juni am schwachsten ist. Die Bedeutung der Befundc fiir die Bekampfung dieser Art wird diskutiert.
Summary Glyphosate was applied at four rates under greenhouse conditions to Avena fatua L. plants at four stages of seed development. Application at anthesis completely prevented the formation of viable seeds. Application five days after anthesis (DAA) of the terminal floret of the panicle significantly reduced seed production at all herbi‐cide rates used, and at 1.76 kg a.i. ha‐1 no viable seeds were produced. When applied 10 DAA, only the highest rate of glyphosate resulted in substantial reduction in number of primary seeds, but seed viability suffered at all herbicide levels. Glyphosate applied 15 DAA still produced a significant decrease in primary and secondary seed production and biomass. Both the viability and the germination rate of seeds from treated plants were significantly affected. When the herbicide was applied to plants 5 DAA, no viable seeds were produced by plants surviving the highest rate, and all rates significantly reduced germination. Glyphosate applied 10 DAA significantly suppressed germination, with 1.76 kg a.i. ha‐1 being the most effective rate. When applied to plants 15 DAA, only the highest rate of glyphosate significantly affected the overall germination of both primary and secondary seeds, but the normal imposition of dormancy was partially blocked in seeds from plants treated with 0.44 and 0.88 kg a.i. ha‐1. These findings are relevant to chemical summerfallow and crop desiccation practices.
The significance of Euphorbia esula L. as a weed is related to its capacity to persist under adverse conditions and to its mode of reproduction. In both these properties, the root system plays an important role. The root system is initially established by seedlings. The seedling has a vigorous primary root with extensive longitudinal growth and considerable cambial activity. Such a root has been designated a "long" root. By contrast, the first lateral roots produced on the primary root have limited growth and no canibial activity. These roots have been termed "short" roots. Thus, the seedling exhibits a "heterorhizic" pattern. Lateral long roots also arise on the primary root of seedlings but their origin is delayed until cambial activity has begun. Such lateral long roots arise much earlier on seedlings growing in denuded areas than on those growing in areas covered by dense vegetation. The mature root system is described in terms of horizontal and vertical long roots, which make up the conspicuous framework of the system, and of the short roats which they produce. Long roots produce shootbuds and the origin of these structures is delayed until cambial activity has started. Short roots do not give rise to shoot-buds. Cambial activity in long roots appears to be connected with bud production and its absence in short raats probably underlies their inability to produce buds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.