摘要:

Comparison of six different populations ofXanthium strumariumgrown under controlled laboratory conditions revealed a general pattern of greater chlorophyll levels with increase in latitude of origin. Indications of ultrastructural differences were found, with plants containing greater chlorophyll levels having more chloroplasts with greater membrane development compared to plants of this species from more southern or lower latitude habitats.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10809.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Ipomoea carnea(Convolvulaceae) possesses two types of extrafloral nectaries, located on the petiole and on the pedicel. These secrete a complex nectar containing sugars and amino acids. The insects attracted to the extrafloral nectaries are predominantly ants and they are relatively abundant throughout the year. A number of incidents of plant defense as a result of the presence of extrafloral nectary visitors at the extrafloral nectaries ofI. carneawere observed and are consistent with the ant‐guard theory of the function of extrafloral nectaries.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10810.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

The location and some morphological, anatomical, and functional aspects of the gravity‐sensitive pulvini of a selected number of grass shoots are examined. There are two distinct gravity‐sensitive regions near the nodal regions of Gramineae. One, the leaf sheath pulvinus, is located at the base of the sheathing leaf bases, and is characteristic of the subfamily Festucoideae. The other, the internodal pulvinus, is located at the base of the internode, a little above the nodal joint. Most members of the Panicoideae possess internodal pulvini, in addition to more or less developed leaf sheath pulvini. Three members of the Oryzoideae examined possess leaf sheath pulvini only, whilePhragmites australis(Arundinoideae) possesses both leaf sheath and internodal pulvini. Leaf sheath pulvini of some grasses develop hairs, cork‐silica cell pairs or stomatal apparatuses over the epidermis while many others are devoid of any such idioblasts. Both the leaf sheath and internodal pulvini of all grasses examined preferentially exclude, or accumulate very little silica, whereas the regions of the shoot immediately above and below the pulvini in these same grasses accumulate large quantities of silica. Pulvini remain unsilicified or poorly silicified throughout their life and even after several days following geotropic bending. Pulvini are also distinguished from the regions above and below them by the lack of lignin in the bundle cap cells. Lignin is found only in the xylem vascular tissue, and this consists of annular and helical vessel elements only. The bundle cap cells are rich in pectin and are described as collenchymatous. All pulvini possess specialized zones of cells containing starch statoliths. In response to horizontal displacement of the shoots, the lower side of the pulvini grows by cell elongation only. The collenchymatous cells stretch in a manner that results in alternately thin and thick regions of cell wall.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10811.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

The attachment of certainAgrobacteriumspecies to moss protonema was examined by scanning electron microscopy. The bacteria cultured with the moss adhered to the protonemal filaments ofPylaisiella selwyniiandFunaria hygrometricathroughout the fixation and washing procedure prior to examination. The number of bacteria adhering per unit length of filament did not correlate with the ability of four species (A. tumefaciens, A. rubi, A. rhizogenes, A. radiobacter) to induce gametophore formation inP. selwynii.Little difference was found between the number ofA. tumefaciensonP. selwyniior onF. hygrometrica, and although this bacterial species induced gametophores onP. selwynii, it had no effect onF. hygrometrica. A. rhizogenes, which is capable of inducing rhizoid formation on bothP. selwyniiandF. hygrometricawithout physical attachment, did associate with filaments of both mosses. Larger numbers ofA. tumefaciensandA. rubi, which induce gametophores or callus, were associated with the spore and germ tube ofP. selwyniithan wereA. rhizogenesorA. radiobacterwhich do not initiate these changes. These results suggest that the germ tube may constitute the site where effective attachment occurs. The number ofA. tumefaciensadhering toP. selwyniiwas greatest at 2–6 h after addition and then decreased by 26 h, raising the possibility that some bacteria lyse following attachment. None of the bacteria adhered to the gametophore walls of either moss, indicating that a change in cell wall surface may occur. The four species ofAgrobacteriumdiffered in their orientation when adhering to the moss. These results suggest that the process of bacterial adherence to higher plant cells inAgrobacteriuminfection is similar to that which we observe in mosses and which leads to developmental changes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10812.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Phytolacca dioicaL., an evergreen tree of the Phytolaccaceae, is one of the species ofPhytolaccawhich shows anomalous secondary thickening in its stem. This mode of thickening has been regarded as successive cambial activity or alternatively, in some more recent interpretations, as thickening by unidirectional activity of a cambial zone. The stem thickening ofP. dioicais of the former type. The cambium produces fascicular strands, showing centrifugal differentiation of xylem and centripetal differentiation of phloem on opposite sides of the cambial layer, and rays are produced between the fascicular areas. In both xylem and phloem the younger elements are closer to the cambium than the older elements. Succeeding cambia arise periodically by periclinal divisions in a layer of parenchyma cells two or three cells beyond the outermost intact phloem derived from the current cambium. Each cambium forms a few parenchyma cells on both sides before it forms derivatives which mature into lignified xylem elements or conductive elements of the phloem. The parenchyma thus formed toward the outside later becomes the site of the origin of the succeeding cambium. Only one or two layers of this phloem parenchyma go on to form the new cambium; the remaining cells accumulate between the outermost phloem and the cortex.P. weberbauerishows stem structure similar toP. dioica. P. meziana, a shrub, shows normal stem structure.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10813.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Prescribed burning under mature Larch/Douglas‐fir forests produced changes in elemental uptake. Elemental analyses of individual species and existing biomass three years post‐burn from hot, medium, and lightly burned sites and unburned controls showed a significant shift in species composition with burn intensity. Few species from hotly burned sites had elevated levels of ions, except phosphorus and iron, but the aboveground shrub and herb biomass did have greater total cations, percent ash, and individual cations (except Ca and Mg) on hotly burned sites. Although the hotly burned sites had the greatest total biomass, only iron, manganese, total nitrogen, sodium, and phosphorus were significantly higher (5% level) in biomass from hot burns compared to control biomass (g/m2basis). Hot burns alter the soil pH to the alkaline range making some elements like iron less soluble and available. Some species growing on hotly burned sites appeared able to alter nutrient uptake making more iron, phosphorus, and other elements available for growth, even with low available levels, compared to control sites. Three‐year‐old western larch (Larix occidentalisNutt.) seedlings were able to accumulate high levels of Fe, K, and P relative to controls.Marchantia polymorphaL. concentrated some ions on hotly burned soils, but it was not possible to locate this plant on unburned areas for comparison.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10814.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Anderson's graphic method of population analysis applied to a number of specimens ofTrichomanessect.Selenodesmiumpoints to introgressive hybridization betweenT. polystromaticumandT. dentatum.The two species, one of which grows in a xeric habitat and the other in a very protected mesic one, tend to maintain their specific integrities in their extreme habitats. Intermediate forms which tend to grow in intermediate habitats give indication of genetic imbalance in the form of diad spore production. Peculiarities of the fern and in particular of the hymenophyllaceous life cycle are discussed in the context of hybridization.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10815.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

The pollen strobilusCordaianthus concinnusis examined as a possible indicator of the basic pattern of vascular architecture in stems of the Cordaitales. Bract traces arise from two points in the stele of the bilateral primary axis and diverge to the regularly arranged, four‐ranked bracts. Tracheids to the axillary secondary shoots arise as two traces that flank the position of bract trace emission. Distally, the secondary shoot traces unite to form a stele that becomes increasingly dissected at successively higher levels. Although radially aligned, these tracheids show thickening patterns on all walls and are not separated by vascular rays; they are therefore interpreted as primary xylem. The traces form sympodia that are similar to those of typical eustelic gymnosperms. Scale traces from the secondary shoots arise by the tangential division of an individual axial bundle and occur in arrangements that range from a ½ to a % spiral. The vascular architecture of these secondary axes is interpreted as the equivalent of that in the stems of extant conifers with spiral phyllotaxis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10816.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Factors controlling the timing of seed germination were investigated in the small succulent winter annualSedum pulchellumMichx. (Crassulaceae) in its natural habitat on unshaded limestone outcrops in northcentral Kentucky. At maturity in early July the dormant seeds are not dispersed but are retained in the fruits on the standing dead plants until September and October. Many, but not all, of the seeds afterripen in the fruits during summer, and at the time of dispersal some of them are dormant and some are nondormant. Germination and annual population establishment occur in September and October from seed reserves that have been in the soil for one or more years and from seeds produced in the current year. Germination of nondormant seeds may be prevented in autumn by lack of the appropriate combination of environmental factors including light, temperature and soil moisture in the seed's microsite. The effect of low winter temperatures on ungerminated seeds in the population is to induce nondormant seeds into secondary dormancy and to prevent afterripening of dormant seeds. Thus, in spring all the seeds in the population's seed reserve are dormant. During spring and summer some of these seeds afterripen, and they germinate in autumn when, and if, germination requirements are fulfilled.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10817.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

The nuclear DNA content of developing barley aleurone cells was examined by Feulgen cytophotometry using the Cytophotometric Data Conversion (CYDAC) system. At no time in their development did aleurone cells exhibit a single peak corresponding to the triploid (3N) amount of DNA. Although considerable heterogeneity was observed at every stage of development, the mean nuclear DNA content approximately doubled from the earliest to the most mature stage.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10818.x

出版商:Wiley    

年代:1977

数据来源: WILEY