摘要:

We investigated the age‐structure of the xylem‐tapping mistletoePhoradendron juniperinumin relation to characteristics of its host tree,Juniperus osteosperma.We first correlated branch structure in the mistletoe with age of the mistletoe infection as determined anatomically; this correlation provided a nondestructive, field method of obtaining age structure information. We then surveyed the mistletoe plants, applying our aging index, within a population of their host trees in southwestern Utah; the majority of mistletoe plants were 2–12 years old. This peak in abundance of mistletoe infections showed no correlation to total annual precipitation within or 1 year previous to the peaks, minimum winter temperature, or to warmer than average winter temperatures. However, there was a positive correlation (r= 0.51,P10 years of age was correlated to a period of below average precipitation, especially during the growing season, but not with cold winter temperatures, which in other studies had been suggested as a factor influencing mortality. We feel that drought may play an important role in influencing mistletoe mortality through its direct affect on host tree water status, but in addition we offer two alternative hypotheses to explain mistletoe longevity; the first is concerned with the relationship between carbon and nitrogen costs and maintaining large leaf areas in older plants, and the second addresses how increased hydraulic resistance in older and larger plants may be too costly for the plant, and stems are abscised.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14444.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Despite the fact that many parasitic and hemiparasitic plant species such as mistletoes are dioecious and occur in both the new and the old world, few data exist on variation in the sex ratio and allocation to reproduction in these taxa. We investigated 1) the sex‐ratio of the xylem‐tapping mistletoePhoradendron juniperinumin relation to its age and position within the canopy of its host treeJuniperus osteosperma,and 2) reproductive effort in relation to the gender and age of mistletoe plants. Our surveys showed thatP. juniperinumhas a male‐biased sex ratio. Despite this predominance of male individuals, females lived longer and had a greater reproductive effort than did males. A statistical analysis of the age distribution data indicated that the peak in the frequency of reproductively mature individuals was later in females than in males. These gender‐specific distributions may have resulted 1) from sequential hermaphroditism (age‐specific sex switching), or 2) because the average age of peak reproduction is later in female individuals. Because sex is genetically determined in a closely related genus of mistletoe and because we have no data to indicate sex switching in this species, we feel that our data support the interpretation that female individuals, on average, show a peak in reproductive vigor at an older age relative to males. While delayed reproduction in females may be favored because reproductive effort and success appear to be age‐dependent in females of this species, both sexes can become reproductively mature relatively early in life. Further, because 1) allocation to reproduction as a function of age increases more rapidly for females of this species relative to males, and 2) because there may be a higher resource cost associated with reproduction in females, we hypothesized that female individuals would be more abundant in the best quality locations within the host tree so as to maximize the opportunity to meet those costs. In spite of the association between gender and some host characteristics, there was no indication that female plants were located in sites most favorable to either their carbon or water balance. We discuss reasons why this may be the case.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14445.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The elastic modulus E, flexural rigidity EI, static loading P, and volume fractions V of tissues of the aerial portions ofPsilotum nudumare examined in terms of two Voigt models: 1) total elastic modulus ETof a branch element is considered the additive property of the elastic modulus of tissues times their respective volume fraction, i.e., ET= (EV), + (EV)2+ … (EV)n, and 2) ETis considered the product of the elastic modulus of cell walls and the apoplastic volume fraction, i.e., ET= EcwVa. The parameters EI and P, together with the length (l) of each branch element are combined into a dimensionless ratio, Pl2/EI (the load parameter L), to describe the relationship between static loading (Pl2) and the ability to sustain loading (EI). The load parameter of branch elements was found to decrease as the level of branching within aerial portions of this race ofPsilotumwas ascended. The magnitude of P also decreased acropetally. However, the decrease in L is primarily due to a disproportionate decrease in EI. The load parameter of the basalmost branch of aerial portions is smaller for larger aerial portions of this race ofP. nudum.Thus, larger specimens are subtended by more rigid branch elements than smaller aerial portions. The Voigt models provide satisfactory approximations of the data from this racePsilotumand indicate that the principal load supporting tissues are the cortical sclerenchyma and other lignified tissues in older (lower branch elements). The mechanics of the three dimensional branching ofP. nudumis extended to consider the aerial portions of some early Paleozoic vascular sporophytes (Algaophyton,Rhynia). Analyses indicate that biomechanical speculation about these fossils is potentially flawed by the ambiguity of anatomical data.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14446.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The floral vascular systems are compared among all six taxa of Saururaceae, including the two species ofGymnothecawhich have not been studied previously. All are zygomorphic (dorsiventrally symmetrical), not radial as sometimes reported, in conformity with dorsiventral symmetry during organogenesis. Apocarpy in the two species ofSaururus(with four carpels and six free stamens) is accompanied by a vascular system of four sympodia, each of which supplies a dorsal carpellary bundle, two ventral carpellary bundles, and one or two stamen traces. The level at which the ventral bundles diverge is the major difference in vasculature between the two species. The other four taxa are all syncarpous, and share some degree of stamen adnation and/or connation. The vascular systems also show varying degrees of fusion. The two species ofGymnotheca(with four carpels and six stamens) are very similar to each other; in both, the ventral traces of adjacent carpels fuse to form a placental bundle, which supplies the ovules and then splits into a pair of ventral strands. The flowers ofHouttuynia cordata(with only three carpels and three adnate stamens) are sessile. Each flower is vascularized by three sympodia; the median adaxial sympodium is longer than the other two sympodia before it diverges to supply the adaxial organs. Three placental bundles also are formed inHouttuynia,but the three bundles differ in their origin. The median abaxial placental bundle diverges at the same level as the three sympodial bundles of the flower, while the other two lateral placental bundles diverge at a higher level from the median adaxial sympodium.Anemopsis californica,with an inferior ovary of three carpels, sunken in the inflorescence axis, and six stamens adnate to the carpels, has a vascular system very similar to that ofHouttuynia cordata.The modular theory of floral evolution is criticized, on the bases of the known behavior of apical meristems and properties of vascular systems. The hypothesis is supported that saururaceous plants may represent a line of angiosperms which diverged very early.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14447.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Comparative ontogeny of the perianth is reported for representative genera and species among mimosoid legumes in order to elucidate intertribal relationships and also relationships to the other two subfamilies of legumes. Initiation of the perianth is acropetal in two whorls. The calyx arises first followed by the corolla. Order of initiation of both calyx and corolla is determined during early ontogeny. Four different types of order of initiation have been found in the calyx: helical, simultaneous within one whorl, bidirectional, and ring meristem. Helical initiation is considered primitive; simultaneous within one whorl, bidirectional, and ring meristem are considered derived. Differences during early organogeny in the calyx among mimosoids result in similar morphologies of the mature calyx which indicates that parallel evolution may have played a major role in evolution of radial symmetry within the group. Order of initiation of the corolla is uniformly simultaneous whorled with one exception. Position of organs is a significant feature which separates mimosoids from caesalpinioids and papilionoids. In mimosoids the median sepal is located abaxially and the median petal adaxially in relation to the subtending bract. In both caesalpinioids and papilionoids the median sepal is located abaxially and the median petal adaxially in relation to the subtending bract. Fusion of the calyx in some taxa can be interpreted as an example of acceleration.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14448.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The vascular system of theHordeum vulgareL. leaf consists of multiple longitudinal strands interconnected by transverse bundles. In any transverse section, the longitudinal strands can be categorized into three bundle types: small, intermediate, and large. Individual longitudinal strands intergrade structurally from one bundle type into another as they descend the leaf. At their distal ends, they have the anatomy of a small bundle. As they descend the leaf, most intergrade into intermediate bundle and then into large bundle types. All strands with large bundle anatomy extend basipetally into the stem. Typically, the other longitudinal strands, which do not intergrade structurally into large bundles, do not enter the sheath, but fuse with other longitudinal strands above the junction of the blade with the sheath. Despite the decrease in number of longitudinal bundles entering the sheath, an increase takes place in the total crosssectional area of sieve tubes and tracheary elements. A linear relationship exists between leaf width and total bundle number in the blade but not in the sheath. Moreover, a linear relationship exists between cross‐sectional area of vascular bundles and both total and mean cross‐sectional area of tracheary elements and thin‐walled sieve tubes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14449.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The purpose of this study was to examine the extent of cellular differentiation in arrested embryos from lethal mutants ofArabidopsis thaliana.The question to be addressed was whether arrested embryos in heterozygous siliques resembled mature wild‐type embryos at the cellular level. Protein bodies were chosen as developmental markers because they appear only during the final stages of embryogenesis. Both the hypocotyl and cotyledons of wild‐type embryos contained protein bodies that became filled with storage protein during the cotyledonary stages of development. Some mutant embryos (emb30) contained normal protein bodies and resembled mature wild‐type embryos at the cellular level. Other mutant embryos (emb22) contained only immature protein bodies and were therefore blocked in both morphogenesis and cellular differentiation. The formation of protein bodies inemb31was normal in the hypocotyl but delayed in the cotyledons. In this case the mutant gene appears to disrupt the timing of both morphogenesis and differentiation. This ultrastructural view of arrested embryos has provided additional information on the nature of developmental arrest that should facilitate the classification of embryonic lethals and the identification of mutants with defects in developmental rather than housekeeping functions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14450.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Mature trees ofAilanthus altissimaproduce one or more potent inhibitors of seed germination and seedling growth. Inhibitor activity is highest in bark, especially of roots, intermediate in leaflets, and low in wood. Crude extracts ofAilanthusroot bark and leaflets corresponding to 34 and 119 mg water extractable material/L, respectively, caused 50% inhibition of cress radicle growth.Ailanthusseeds also contain one or more inhibitors. These are bound within the seed by the pericarp but diffuse into water agar when the pericarp is removed. The inhibitor(s) could readily be extracted fromAilanthustissues with methanol, but not dichloromethane, indicating polar characteristics.Ailanthusleaflets had highest inhibitory activity during expansion in spring, whereas activity of trunk bark peaked just before emergence of leaves. This pattern suggests transport of allelochemicals from bark into new leaves. A comparison of seven plant species for sensitivity to the inhibitor(s) fromAilanthusroot bark showed little selectivity, although velvetleaf was somewhat more resistant. The inhibitor(s) fromAilanthusroot bark exhibited strong herbicidal effects when sprayed pre‐ and postemergence on plants in soil in the greenhouse. Postemergence effects were striking, with nearly complete mortality of all species, except velvetleaf, at even the lowest doses tested. The results suggest the allelochemical(s) fromAilanthusmay have potential for development as natural‐product herbicides.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14451.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

We compared the rate of pollen tube growth following self‐ and cross‐pollinations both among and within flowers of two clones ofDianthus chinensisL. For among‐flower comparisons, both styles of a flower were pollinated with either self‐ or cross‐pollen. Within‐flower comparisons were made between the two styles of the same flower, one of which was self‐pollinated and the other cross‐pollinated. Comparisons between flowers indicated that self‐pollen grew slower than cross‐pollen in both clones. However, differences in the growth rate of pollen tubes from self‐ and cross‐pollinations were greater when comparisons were made between the two styles of the same flower than when pollinations were made in different flowers. These results suggest the existence of interstyle interactions in pollen tube growth.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14452.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Cycads have been the subject of a wide variety of botanical studies. However, nothing is known of the genetic structure of their populations. Seeds were collected from five populations of the common Australian cycadMacrozamia communisalong a north to south transect through its 500‐km‐long range in eastern New South Wales. Leaf samples from seedlings grown from those seeds were the subject of isozyme analysis. Nine of the 18 isozyme loci studied were polymorphic. Levels of polymorphism varied among loci and among populations. The three southern‐most populations were genetically similar to one another but well differentiated from the other two. The levels of species‐wide genetic diversity observed forM. communiswere relatively low compared with those of other gymnosperms and angiosperms. On the other hand, the levels of spatial differentiation were relatively high, especially compared with other gymnosperms.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14453.x

出版商:Wiley    

年代:1990

数据来源: WILEY