摘要:

Lateral roots ofTypha glaucaarose from the pericycle of the parent adventitious root. Periclinal divisions of the pericycle gave rise to two layers; the outermost initially produced the ground meristem and protoderm, and the innermost produced the procambium. The immature endodermis of the parent root contributed to the early stages of the root tip as an endodermal covering. Prior to emergence, the ground meristem/protoderm produced cells into the endodermal covering. After emergence, the endodermal covering was replaced by a calyptrogen, which was derived from the ground meristem/protoderm and which, in turn, formed the rootcap. A typical monocotyledonous three‐tiered meristem was then produced. An outer ground meristem also arose before emergence to form a hypodermis in many lateral roots; in these, crystalliferous cell production began in midcortex cells before emergence, and a small aerenchyma developed in their cortices. The rootcap columella stored small amounts of starch shortly after emergence. Lateral roots ofT. glaucawere smaller than their parental adventitious roots; they normally had only two to six poles of xylem and phloem, and the cortex was less than six cells across. During 1–3‐cm elongation, the lateral root apical meristem and mature regions narrowed, stored starch disappeared, fewer crystals formed, aerenchyma production ceased, and the roots stopped elongation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14460.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Cytogenetic evidence suggests thatTripsacum andersoniimay be a natural hybrid betweenZeaandTripsacum.In this paper we show sequences that hybridize to the transposable elementsMulandSpmare found inT. andersoniiand allZeaspecies examined. However, no hybridizable sequences are observed in the five otherTripsacumspecies surveyed. These results suggest thatMuandSpmelements became components of theZeagenome after the divergence ofZeaandTripsacum,and they strongly support the cytological evidence thatT. andersoniiis aZea‐Tripsacumhybrid. Examination of nuclear ribosomal genes ofT. andersoniialso supports the hybridization hypothesis and identifies theZeaparent asZea luxurians.TheTripsacumparent could not be conclusively identified, but the ribosomal gene data suggest that the species ofTripsacumsectionFasiculatamost closely resembleT. andersonii.Restriction site patterns of two chloroplast DNA sequences indicate that the maternal parent was a species ofTripsacum.These results are complemented by morphological evidence regarding the origin ofT. andersonii.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14461.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Epidermal differentiation in primary roots ofZea mayswas divided into six cell types based on cellular shape and cytoplasmic appearance. These six cell types are: 1) apical protoderm, located at the tip of the root pole and characterized by periclinally flattened cells; 2) cuboidal protoderm, located approximately 230μm from the root pole and characterized by cuboidal cells; 3) tabular epidermis, located approximately 450μm from the root pole and characterized by anticlinally flattened cells; 4) cuboidal epidermis, located approximately 900μm from the root pole and characterized by cuboidal cells having numerous small vacuoles; 5) vacuolate cuboidal epidermis, located approximately 1,500μm from the root pole and characterized by cuboidal cells containing several large vacuoles; and 6) columnar epidermis, located approximately 2,200μm from the root pole (i.e., at the beginning of the zone of elongation) and characterized by elongated cells. We also used stereology to quantify the cellular changes associated with epidermal differentiation. The quiescent center and the apical protoderm have significantly different ultrastructures. The relative volume of dictyosomes increases dramatically during the early stages of epidermal differentiation. This increase correlates inversely with the amount of coverage provided by the root cap and mucilage.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14462.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Thirty‐five flowering individuals of the orchidCyclopogon cranichoideswere marked in 1986, and their leaf area, number of flowers, and number of fruits were recorded from 1986 to 1989. In 1986 and 1987 all the flowers on 20 individuals were hand‐pollinated. The number of plants with above‐ground growth steadily decreased by about 20% each year. In some cases there was evidence that disappearance of plants was not due to mortality but to a transition into a subterranean state. Small plants were most likely to make this transition. Flower number was significantly associated with plant size. Fruiting success was pollinator‐limited throughout this study; fruit set of hand‐pollinated individuals was higher than 96%, whereas natural fruit set ranged from 26% in 1987 to 62% in 1988. Fruit set did not have any effect on growth or reproduction the following year.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14463.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Excised stem segments of vines had higher specific hydraulic conductivities (flow rate per pressure gradient per stem transverse area) than did trees during the dry season in a deciduous forest in Jalisco, México. Vine species averaged from 2.7 to 203 10‐3m2MPa‐1s‐1and tree species from 0.8 to 5.1 10‐3m2MPa‐1s‐1. Only three of the 20 species retain their leaves during part or all of the dry season, and these included the vine and the tree with the lowest conductivities within their growth forms. An index of the mean diameter of the six widest vessels per sample was positively and significantly correlated with specific conductivity for the vines but not the trees. Stem density (g cm‐3, dry weight/wet volume) was not correlated with either specific conductivity or vessel diameter index for vines or trees.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14464.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Ateleia herbert‐smithiiis unique among legumes in being a wind‐pollinated tree; carpellate and staminate flowers are restricted to different trees. Development of the two floral morphs, however, is essentially the same except for smaller carpels in functionally staminate flowers and failure of pollen formation in the anthers of functionally carpellate flowers. The floral development ofAteleia herbert‐smithiiis highly atypical among papilionoids and the tribe Sophoreae. Order of organ initiation is: sepals, solitary petal, carpel, and lastly all stamens in erratic order. Sepal order is unidirectional from the abaxial side, the normal pattern for papilionoids. Only one petal, the vexillum or standard, is initiated. Subsequent initiation is completely different from the usual unidirectional pattern of most papilionoids. A meristem ring forms, delimiting the solitary carpel centrally. Ten stamen primordia are initiated on the meristem ring, first laterally, then adaxially, and lastly abaxially. There is a tendency for antesepalous stamens to form before the antepetalous ones. The loss of four of the five petals is thought to alter drastically the subsequent organogeny as to position of organs and their order of initiation. Carpel initiation inAteleiais precocious, but not uniquely so among legumes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14465.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Determinate growth in an organ can reduce the mechanical liability of dynamic wind loadings. This hypothesis was examined for the peduncles ofAllium sativumgrown under protected and unprotected field conditions and in the glasshouse. The extent to which the lengths of peduncles approach their critical buckling lengths lcr was correlated with the extent to which peduncles were perturbed mechanically. Glasshouse‐grown plants that were protected from dynamic loadings (wind or handling) produced peduncles with low ratios of critical to actual peduncle lengths (lcr/1 = 1.11 ± 0.07); field‐grown, unprotected plants had lcr/1 = 1.85 ± 0.29; while plants grown in the field but protected from the wind had lcr/1 = 1.29 ± 0.15. Statistical analyses indicated that peduncle length was the only morphometric parameter examined to significantly differ among plants grown under the three conditions. The frequency distributions of critical (buckling) stress for each of the three populations of peduncles differed; that of the unprotected population conformed to a three‐parameter Weibull distribution.Allium sativumexhibits thigmomorphogenesis, i.e., mechanical forces influence the extent and nature of organogenesis. Unlike other thigmomophogenetic species, however, the determinate growth of peduncles did not influence peduncle girth or the elastic (Young's) modulus of tissues. Thus, the extent to which vertical growth proceeded determined the design factor for dynamic loading in these reproductive organs. The design (“margin of safety”) factors ofA. sativumpeduncles grown under the three different conditions and calculated from lcr/1 were remarkably similar to those specified for engineered columns of wood subjected to stress durations differing in magnitude.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14466.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The B genome ofGlycinesubgenusGlycinecomprises three diploid species whose monophyly is supported by morphological, crossing, and chloroplast DNA (cpDNA) data. Previous cpDNA studies indicated low levels of divergence among these taxa and failed to resolve cladistic relationships among them. More intensive studies of cpDNA variation were initiated, using additional restriction endonucleases and accessions. Results from cladistic analyses of over 50 restriction site characters indicate that there is considerable cpDNA polymorphism within this group of species, with a minimum of 27 plastome types occurring among the 74 accessions sampled. Levels of homoplasy observed in this group are relatively high (15%) for closely related congeneric species. There is only limited congruence between plastome type and taxonomic classification based on morphological characters. Explanations for this lack of concordance include: 1) the early state of taxonomic understanding in this group, 2) lack of resolution in the cpDNA tree caused by homoplasy and the small number of synapomorphic characters, 3) introgression among these interfertile, often sympatric taxa, and 4) maintenance of ancestral cpDNA polymorphisms resulting in shared plastomes among species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14467.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Pollen apertures were analyzed among the subfamilies Persoonioideae (seven genera; ca. 95 spp.), Sphalmioideae (one genus; one spp.), and Camarvonioideae (one genus; two spp.). Pollen was examined by light microscopy, cryosection, and transmission electron microscopy. Completed studies of pollen apertures among Grevilleoideae (ca. 40 genera; ca. 800 spp.), one of two major subfamilies in Proteaceae, provide a basis for comparison and analysis of aperture evolution among these subfamilies. Aperture characters within Persoonioideae are unique among Proteaceae examined to date. Five distinct aperture types occur among the three subfamilies, three of which (Placospermum, Persoonia, Bellendena) are restricted to Persoonioideae. Sphalmioideae and Camarvonioideae each exhibit a unique aperture organization. The most primitive aperture organization, and one unique toPlacospermum,exhibits three main features: 1) a thin, granular endexine continuous around the grain; 2) a heterogeneous foot layer throughout the grain with increased disruptions at the aperture; and 3) only slight differences in exine characters between apertural and nonapertural regions. ThePersooniaaperture type represents the next stage of aperture evolution which involves loss of endexine, restriction of a heterogeneous foot layer to the aperture, and marked differences in exine characters between apertural and nonapertural regions. The uniformly homogeneous ektexine in both nonapertural and aperture regions inBellendenahas developed independently.Sphalmiumexhibits a primitively thin granular endexine though the restriction of endexine to the aperture is a derived condition.Carnarvoniaexhibits several pollen characters also found among Grevilleoideae including: 1) a homogeneous nonapertural ektexine; 2) a slightly heterogeneous apertural ektexine; 3) a lamellate/granulate endexine organized into irregularly shaped “clumps” clustered around the aperture; and 4) a clear demarcation between apertural and nonapertural exine. These characters support the hypothesis thatCarnarvoniamay have diverged early from the pre‐Grevilleoids.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14468.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The morphology, ontogeny, and vascular anatomy of the staminate inflorescences and florets of seven species ofAllocasuarinaare described. The generally terminal but open‐ended inflorescences occur on monoecious or staminate dioecious trees and consist of whorls of bracts, each subtending a sessile axillary floret. Each floret consists of one terminal stamen with a bilobed, tetrasporangiate anther enclosed typically by cuculliform appendages, commonly considered bracteoles, an inner median pair and an outer lateral pair. The mature stamen is exerted, the anther is basifixed and is extrorsely dehiscent. In early development of a male inflorescence very little internodal elongation occurs and enclosing cataphylls appear. The inflorescence apex is a low dome with a uniseriate tunica and a small group of central corpus cells. Bract primordia are initiated by periclinal divisions of C1followed by further divisions of the corpus and anticlinal divisions in the tunica. The bracts are epinastic and become gamophyllous except apically by cell divisions in both sides of each primordium. Stomata are restricted to the axis furrows and the abaxial tips of the bracts. The axillary florets arise in acropetal succession initiated by periclinal divisions in C1accompanied by anticlinal divisions in the tunica. The lateral floral appendages are also initiated by C1followed by anticlinal divisions in the tunica. They become adnate basally later with the subtending bract. The median sterile appendages are initiated in a manner similar to the initiation of the outer appendages. The stamen is initiated by divisions in the outer layers of the corpus and in the tunica, and then develops first by apical growth followed by intercalary growth. The vascular system of the inflorescence is identical to that of the vegetative stem. Each floret is supplied by a single bundle that has its source in a branch from each of the two traces supplying a bract. Six bundles arise from the floral bundle; four of these terminate in the base of the stamen and two form an amphicribal bundle that supplies the anther. Pollen is binucleate, 3‐ to 7‐porate. The exine is tegillate.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb14469.x

出版商:Wiley    

年代:1990

数据来源: WILEY