摘要:

Low productivity rate and relatively bare areas occur under sycamore, hackberry, red oak, and white oak trees, even though several herbaceous species may grow well under elm trees in the same community which cast just as dense shade. No significant differences were found in amounts of most mineral elements andpH sampled under sycamore, hackberry, red oak, and white oak trees as compared with control soils under elm trees in the adjacent plots. Percent soil moisture was consistently higher under all test trees than under elm trees throughout the growing season. Thus the low productivity rate and relatively bare areas under sycamore, hackberry, red oak, and white oak trees were not due primarily to the factors stated above. Decaying leaves, leaf leachate of all four test species, and soil collected from under test trees significantly reduced seed germination, radicle growth, and seedling growth of selected herbaceous species. Several growth inhibitors, chiefly phenolics, were isolated and identified from sycamore, hackberry, red oak, and white oak leaves and the soils under them. Thus it appears that the low productivity rate and destitute growth under test tree species are due to allelopathy. Ecological significance of allelopathy in a community is discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb11781.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

Protosalviniahas a large thallus on whichP. arnoldiiandP. ravennaforms develop. Light and scanning electron microscopy of Upper Devonian compression forms ofProtosalvinia arnoldii, P. ravennaandP. furcatafrom the Ohio Shale of Kentucky and Ohio, statistical analyses of their cellular dimensions and patterns, and mathematical constructs of thallus shapes and sizes indicate thatP. ravennaandP. furcataforms could be ontogenetically derived from aP. arnoldiistage. Tetrads, interpreted as the meiotic sporangial products, are morphologically identical for the three forms; tetrads contain a sporopollenin fraction and occur singly in closed, hypodermal conceptacles. Solitary, multicellular, stalked clavate structures occur in similar closed chambers. Fossil thalli are composed of hydrocarbons with some lignin‐like compounds interpretable as cuticular in nature.P. ravennaandP. furcataare morphological forms of a single species showing phenotypic plasticity within an onshore‐offshore paleoecological gradient. The form of thallus and the resistant spores are interpreted as adaptations to a littoral environment. The morphology and mode of reproduction ofProtosalviniasuggest a heteromorphic diplobiontic life‐cycle, similar to the Heterogeneratae (Phaeophyta).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb11782.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

Sieve elements of various ages were examined in petioles and midribs ofPlatycerium bifurcatum(Cav.) C. Chr. andPhlebodium aureum(L.) J. Sm., only older ones in similar parts of leaves ofPolypodium schraderiMett. andMicrogramma lycopodioides(L.) Copel. Nacreous walls apparently are formed by most, if not all, protophloem and metaphloem sieve elements in all four species. InPlatyceriumandPhlebodiumnacreous wall formation is closely correlated with the appearance of numerous membranes or vesicles in the region of the wall. These extracytoplasmic membranes apparently are derived from protrusions of the plasmalemma. After the nacreous layer is fully thickened, many endoplasmic reticulum (ER) membranes apparently end up outside the plasmalemma ofPlatycerium, where they degenerate and gradually intergrade in appearance with the fibrillar material comprising the nacreous thickening. InPhlebodium, Polypodium, andMicrogrammathe ER forms multivesicular bodies. As the cells approach maturity, the membranes delimiting the multivesicular bodies fuse with the plasmalemma and their vesicular contents, which are not discharged into the region of the wall, disappear. Gradually, the nacreous layer decreases in thickness and disappears. At maturity the enucleate sieve‐element protoplasts of all four species are essentially similar. They are lined by a plasmalemma and a parietal, anastomosing network of ER and contain both plastids and mitochondria. The plastids inPolypodiumandMicrogrammaare chloroplasts, but those inPlatyceriumandPhlebodiumlack grana and intergrana lamellae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb11783.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

The diatom flora of the cavern system of Timpanogos Cave National Monument was investigated. Diatoms were found throughout the cave system and were distributed according to moisture and natural openings. Twenty‐six species were identified and described, including eight not previously collected from caves and four new records for the state of Utah.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb11784.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

Sixteen species of cellular slime molds were isolated from Southeast Asian forest soils. Ten of these,Dictyostelium mucoroidesBrefeld,D. purpureumOlive,D. polycephalumRaper,D. lacteumvan Tieghem,D. rhizopodiumRaper and Fennell,D. lavandulumRaper and Fennell,D. vinaceo‐fuscumRaper and Fennell,D. coeruleo‐stipesRaper and Fennell,Polysphondylium violaceumBrefeld, andP. pallidumOlive have been previously described and are well‐recognized species occurring in other parts of the world. Two, one in the genusDictyosteliumand one belonging to the family Guttulinaceae, are considered species by the author but have not been formally described. Four are described in this paper as new:Dictyostelium intermedium, D. multi‐stipes, D. bifurcatum, andAcytostelium subglobosum.A new varietypapilloideumofD. lacteumis also described. One other discovery of special interest is an isolate ofPolysphondylium violaceumwhich produces abundant macrocysts, now known to be the sexual stage in the life cycle of cellular slime molds.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb11785.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

Soils were collected from thirteen tropical forest sites in the Southeast Asian countries of Singapore, Malaysia, Thailand, Indonesia, and the Philippines. Soil dilutions of 1:25 were prepared and cellular slime molds identified from clones which subsequently developed when 0.5 ml of the dilutions were spread on dilute hay infusion agar plates seeded with pregrown bacteria (Escherichia coli#281). A total of 2998 clones representing sixteen species was produced by this procedure. Species were tabulated in order of ecological importance which was based on their frequency, relative density and presence throughout the area of study. Five species were very common and widespread. Four species were less common but occurred in about half the forest sites; the remaining seven species, including all but one of the new forms, were much more localized in distribution and were considered rare. These results were comparable to those obtained from studies in the American tropics. Diversity was similar and the important (common and widespread) species were the same in both areas. In general, those species that appeared to be endemic to either area belong among the rare species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb11786.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

Chromosome numbers were determined for 63Anthuriumspecies. Thirty‐eight of these were newly determined. Generally the present work confirmed existing chromosome counts when these were available for comparison. The most common somatic chromosome number found was 30, but counts ranged from 2n = 20 to 90. In a few instances conflicting counts were obtained. B chromosomes were found frequently in Sect.Cardiolonchiumand varied in number from one to three. Four polyploid series were evident from all available counts: 20‐40, 24‐30‐48‐84, 28‐56 and 30‐60‐90‐ca 124. Most species were part of the polyploid complex based on 30. Although species were not observed with n = 5, 6 or 7, movement among the basic numbers was considered to have occurred at this level. The relationship among these basic numbers and n = 15 (x2) is still obscure.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb11787.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

This paper describes inflorescence structure, including organogenesis of the panicle and flower clusters and vasculature of flowering branches, for two species ofPtychosperma, a genus of arecoid palms. The inflorescence is an infrafoliar panicle with up to four orders of branches in a spirodistichous arrangement conforming to an irregular one‐half phyllotaxy. The primordium of the inflorescence is crescentic and the apex has two tunica layers, a group of central cells, and a rib meristem. The distal flower‐bearing parts or rachillae of all branches develop acropetally early in ontogeny and are vertically oriented in the bud. Although these rachillae terminate branches of different sizes and orders, they are similar in size and in number of flower clusters produced. Internodes and lower parts of branches develop later. Bracts of four types are produced: a prophyll and empty peduncular bract, bracts which subtend lateral branches, bracts subtending triads, and floral bracteoles. The prophyll and peduncular bracts are tubular and completely closed around all branches until about three months before the flowers reach anthesis. Bracts subtending lateral branches and those that subtend triads enlarge by small amounts of apical, adaxial, and marginal growth to cover subtended apices during early ontogeny, but are small to absent at maturity. Flower clusters are triads of two lateral staminate and a central pistillate flower. Organogenesis indicates that the triad is a sympodial unit. Flowers develop successively, each floral apex bearing a bracteole that subtends the next flower. The vasculature of the inflorescence may be divided into two systems. Bundles of the main axis extend acropetally into the vertically oriented branches as they are initiated and form a central cylinder of larger bundles in each branch. Flower clusters are supplied by a peripheral system of smaller bundles that develop later in relation to the developing floral organs. Bundles of the peripheral system branch frequently, but branching levels are irregular. The irregular branching of peripheral bundles appears related to the phyllotaxy of the flower clusters and the random right or left position of the first flower of the triad. The level of branching of a bundle may depend on the position of a floral primordium with respect to an existing procambial strand. Three (‐4) bundles supply each staminate flower and six (‐10) the pistillate flower. The histologically specialized inflorescence has stomata and contains abundant starch. Tannins and raphides, spherical silica bodies, and various forms of sclerenchyma appear in sequence and apparently provide support and protection during the long exposure of the branches.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb11788.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

The staminate flower ofPtychosperma mooreanumandP. gracilehas three imbricate sepals, three valvate petals, an androecium of 9–13 or 27–32 stamens, and a lageniform pistillode. Pistillate flowers have three imbricate sepals, but the three petals are also imbricate, and the three (‐seven) staminodes are irregular and sometimes basally fused. The ovoid pseudomonomerous pistil has a single locule with a pendulous ovule and three small distal stigmatic lobes. All floral organs are initiated by periclinal divisions in the second tunica layer of the floral apex, with divisions in the outer layer of the cortex also apparent in the initiation of stamens and staminodes. Primordia of floral organs differ in shape but can be related to those of other palm flowers. Sepals are initiated and develop successively, and during floral organogenesis are horizontally oriented covering other organs. Petals are also initiated successively, but rapidly attain equal size. Petals of staminate and pistillate flowers are initially similar, but subsequent prolonged activity of marginal meristems results in widely imbricate petals in pistillate flowers. The polyandric androecia are clearly trimerous. As stamen initiation commences, the apex is divided into sectors or primary primordia consisting of a narrow ridge opposite each sepal and a large triangular bulge opposite each petal. Stamens arise as secondary primordia in alternating antesepalous and antepetalous cycles. Variation in number of stamens is due primarily to variation in the number of primordia that arise in the wider lower antepetalous loci. The primordium of the pistillode is girdling but becomes trilobed later. The gynoecium is initiated as three unequal crescentic carpel primordia that are united by zonal growth early in development. A procambial strand develops acropetally into each floral organ, and additional strands are formed as each organ increases in size. Floral organs are histologically specialized. The appearance of tannins, raphides, and silica and the maturation of sclerenchyma are basipetal within each floral organ.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb11789.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

Regrowth from wounded stipe explants ofSargassumcan be divided into four stages based on cytological changes. The first stage involves changes associated with the wound reactions and the formation of a wound epidermis. The second stage includes the formation of a well defined medullary pit with meristematically active cells around its periphery. Several “bud primordia” are also formed which begin to grow by cell division towards the wound surface. The third stage involves a period of internal tissue differentiation in the “bud primordia” such that mitotic activity is localized in the bud tip and the basal cells grow by cell elongation. The fourth stage marks a major change in the morphology of the regeneration branch from a tubular structure to that of a flattened blade. This change in morphology is preceded by the formation of an apical pit around which the flattened growth appears to be organized.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb11790.x

出版商:Wiley    

年代:1976

数据来源: WILEY