ACROPETAL LEAF DIFFERENTIATION IN QUERCUS RUBRA (FAGACEAE)

Northern red oak (Quercus rubra L.) leaves were shown to mature progressively from base to tip of the lamina based on studies of growth rates, anatomical differentiation, and ¹⁴C-transport. Lamina expansion in both length and width ceased in the basal quarter of the leaf before the apical quarter. Cell expansion and tissue differentiation were more advanced at the base than at the tip of leaves at 10%–20% of full expansion. Physiological data supported the morphological and anatomical data. Sink activity was examined by following the distribution of ¹⁴C imported into sink leaves with direct vascular connections to the source leaf to assure uniform assimilate supply to the sink leaves. Leaves approximately 50% of full expansion imported five to seven times more ^l4C-assimilates into the tip than into the base of the leaf, consistent with continued sink activity in the leaf tip after import by the leaf base has ceased. Transport of ¹⁴C from portions of the leaf, indicating source activity, occurred first in the basal portion of the lamina. The base functioned as a source at approximately 40% of full expansion; the tip, at approximately 60%. Thus, northern red oak displays an acropetal pattern of leaf expansion and differentiation, unlike the more typical pattern of basipetal leaf development defined in many other dicotyledonous genera with simple leaves.     

REPRODUCTIVE MORPHOLOGY OF QUERCUS (FAGACEAE)

Details of inflorescence, floral, and fruit morphology have been studied in more than 120 species of Asiatic and American Quercus. Of the two subgenera, subgenus Cyclobalanopsis has fewer species but greater diversity of reproductive morphology than subgenus Quercus. Some character states of subgenus Cyclobalanopsis, such as more numerous stamens, male flowers sometimes grouped in dichasia, abortive ovules well developed, prominent intrusive septae in the nut, and lamellate cupules, are shared with Lithocarpus. The diversity of cupular sizes, coverage, and ornamentation raises questions about the adaptive nature, ecological function, and phylogeny of the cupule, which clearly has by now evolved as a structure with its own qualities.     

POSITIONAL AND SEASONAL VARIATION IN OAK (QUERCUS; FAGACEAE) LEAF MORPHOLOGY

Within-tree and seasonal variation in quantitative characters of oak leaves were evaluated by factorial analysis of variance. All linear and areal measurements illustrate marked within-tree and seasonal variation. Numbers of lobes and bristle tips and primary vein angle appear relatively stable within trees and among seasons. In many instances, size-correction reduces both within-tree and seasonal variance to nonsignificant levels. However, all characters do not illustrate the same trends either within trees or across the seasons. The results have important implications for those attempting to evaluate among-tree and among-population variation.     

ELEVATIONAL VARIATION IN FOLIAR FLAVONOIDS OF QUERCUS RUBRA L. (FAGACEAE)

Foliar extracts of high elevation Quercus rubra contain 20 major flavonol-3-0-glycosides based primarily on the aglycones myricetin, quercetin, and kaempferol. These compounds display an altitudinal cline in the Appalachian mountains, with quercetin-rich low elevation chemotypes intergrading into myricetin-rich high elevation forms. These chemotypes appear to be correlated with previously documented variation in foliar morphology. The degree of interpopulation variation also differs with elevation. At higher elevations flavonoids differ only quantitatively between sites, while below 3,000 ft there is site-to-site variability in the hydroxylation level of the aglycones.     

LIGNOTUBER ONTOGENY IN THE CORK-OAK (QUERCUS SUBER; FAGACEAE) I. LATE EMBRYO

Changes at the cotyledonary node of the cork-oak (Quercus suber L.) were examined during the embryo maturation phase using light microscopy and scanning electron microscopy techniques. During the maturation phase the embryo axis elongates by diffuse growth, the apical meristem forms the first leaf primordia, and the radicle meristem remains inactive. The primary axis of the embryo bears, axillary to the cotyledons, in the range of five to seven pairs of lateral buds at differing stages of development. Two or three pairs of these buds are visible, occurring on the upper unfused portion of the embryonic axis, while the remaining buds are hidden by the fused cotyledonary tissues. Lateral buds develop from clusters of cells in the peripheral meristem forming a shell zone delimiting the bud meristem. Lateral buds do not undergo much development until germination begins. The results are discussed with reference to the possible role of the cotyledonary node as the source of the lignotuber in the cork-oak.     

LATE OVULE AND EARLY EMBRYO DEVELOPMENT IN QUERCUS GAMBELII

The ovary of Quercus gambelii is tricarpellary and trilocular; each locule contains two anatropous, bitegmic ovules. The formation of a caecum from a chalazal extension of the embryo sac was observed. A central resistant column of cells, which exhibit some continuity with the vascular trace supplying the ovule, remains protruding into the embryo sac from the chalaza until the later stages of embryo development. Early embryogeny is characterized by a nearly vertical first division with both of the derivative cells contributing to the building of the embryo proper. Such observations suggest that the embryogeny of Quercus should be placed in the Piperad or Asterad type rather than the Onagrad type as has been the practice.     

POLLINATION,FERTILIZATION AND OVULE ABORTION IN OXALIS MAGNIFICA

Pollination, fertilization and ovule abortion were studied in Oxalis magnifica (Rose) Knuth, a strongly self-incompatible herb that regularly matures only a fraction of its ovules. Examination of cleared ovules indicated that among 9 individuals the average number of ovules fertilized ranged from 48–92%. The remaining ovules either failed to produce female gametophytes, or more commonly contained unfertilized female gametophytes, despite large numbers of compatible pollen grains that were placed on stigmas. Abortion of fertlized ovules could be detected first by the flattened and enlarged appearance of the endosperm nuclei, followed by visible deterioration of the embryo. Among individuals the rate of embryo abortion varied from 3.4–47.9%. At lower levels of pollination an almost one-to-one relationship existed between the number of pollen grains placed on stigmas and the number of seeds matured in the capsule. No threshold number of pollen grains necessary for successful pollen tube growth and fertilization could be demonstrated. Reduction in seed number through embryo abortion provides an opportunity for selection among developing seeds. The potential for this form of selection varies widely among individuals of Oxalis magnifica, which showed a 14-fold variation in the average percentage of aborted ovules.     

LEAF GAS EXCHANGE IN QUERCUS MACROCARPA (FAGACEAE): RAPID STOMATAL RESPONSES TO VARIABILITY IN SUNLIGHT IN A TREE GROWTH FORM

Responses in net photosynthesis (A), stomatal conductance to water vapor (g), and leaf xylem pressure potential (ψ) were measured in the deciduous tree Quercus macrocarpa during alternating periods of sun (photosynthetic photon flux, PPF > 1,500 μmol m^-2 sec^-1) and shade (ca. 350 μmol m^-2 sec^-1 simulating cloud cover). Measurements were made on trees growing at the gallery forest-prairie edge on the Konza Prairie Research Natural Area in northeast Kansas. The region is near the westernmost extension of the range of Q. macrocarpa where this species experiences significant seasonal water stress (minimum ψ < -2.9 MPa). Quercus macrocarpa was chosen for study because it has relatively high A (15 μmol m^-2 sec^-1) and g (300 mmol m^-2 sec^-1) in contrast to the deciduous and evergreen subalpine trees previously studied. Both trees and large saplings of Q. macrocarpa responded to alternating several minute periods of sun and shade with relatively rapid changes in A and g. Reductions in g (110 mmol m^-2 sec^-1) during shade periods lowered transpirational water losses (E) by 13% (and reduced A by 5%) relative to estimates of A and E made assuming g remained constant. Partial stomatal closure during shade was correlated with moderate enhancement in ψ (0.31 MPa) in Q. macrocarpa. However, greater increases in ψ were measured in adjacent prairie grasses exposed to similar periods of shade (0.72 MPa in Andropogon gerardii, 0.61 MPa in Sorghastrum nutans). Reduced variability in ψ in tree growth forms may reflect greater buffering of water relations associated with the large size of trees, the amount of tissue devoted to water storage, and differences in hydraulic resistance relative to herbs. Nonetheless, the gas exchange and water relations responses in Q. macrocarpa were much more similar to those previously measured in herbaceous subalpine and grassland species than to those documented for subalpine trees. Thus, rapid gas exchange responses to variable PPF may also occur in tree growth forms.     

CONE AND OVULE DEVELOPMENT IN SCIADOPITYS (TAXODIACEAE-CONIFERALES)

Ontogeny of seed cones of Sciadopitys, with special reference to the ovule-supporting structure, is studied in material collected in Japan and Massachusetts. Cones are initiated as lateral or terminal structures in summer and complete the formation of most organs before winter. Bract development is well advanced before ovule-supporting structures are initiated. Continued cone development involves the formation of a narrow ridge of tissue in the axil of each fertile bract. This ridge develops a series of nine (but up to 12) apical lobes in centrifugal order, each of which is the primordium of a future tooth on the ovuliferous scale. Ovules are initiated as outgrowths of the adaxial surface of each lobe so that there is a one-to-one ratio between lobes and ovules. Intercalary extension of the ovuliferous scale itself (distally) and the common base of the bract and ovuliferous scale (proximally) greatly extends the complex. The ovuliferous scale eventually exceeds the subtending bract and its apex becomes recurved. Bracts each have a single trace, but each ovuliferous scale has a pair of traces that proliferate distally to irrigate ovule and scale lobe. Intercalary growth results in recurvature of the ovule trace. The organization of the cone is directly comparable with certain Permian fossils. Sciadopitys also seems unique within the Taxodiaceae in its centrifugal development of the ovule-supporting complex.     

OVULE AND EMBRYO DEVELOPMENT IN DORITIS PULCHERRIMA (ORCHIDACEAE)

The placental ridge began to proliferate 10 days after pollination. Megaspore mother cell underwent meiosis to form two dyads at first division. At 50 days two megaspores and generating dyad were formed by second division. The functional megaspore divided successively three times to form an eight-nucleate embryo sac at 60 days. Double fertilization occurred forming the zygote and endosperm initial cell. However, the endosperm initial cell degenerate soon thereafter. The zygote divided to form a terminal cell, the middle cell and suspensor initial cell at 70 days. The terminal and middle cells successively divided to form a multi-celled embryo up to 120 days after pollination. Histochemical study showed that the stainability of DNA, RNA and total proteins were almost constant during ovule and embryo development. Stainability of total carbohydrates decreased.     

壳斗科植物摘录(Ⅴ)

<正> 壳斗科 FAGACEAE 锥属 Castanopsis Spach 苦槠钩锥 Castanopsis kuchugouzhui Huang et Y. T. Chang, hybr. nov. [Castanopsis sclerophylla (Lindl.) Schott. ×C. tibetana Hance] Castanopsis tibetana × sclerophylla Huang et Y. T. Chang in Guihaia 10(1) :7. 1990.     

西藏壳斗科的地理分布

在野外考察、分类清理和修订的基础上讨论了西藏壳斗科的地理分布。自然分布的西藏壳斗科植物,共３属３３种,集中分布于藏东南的河谷地带和喜马拉雅山脉的聂拉木县,印度栲、刺栲、喜马拉雅石栎和西藏石栎是这些地区海拔２００米以下群落建群种;通麦栎、俅江栎和薄片青冈是西藏海拔１８００－２５００米地段森林植物被的建群种;硬叶高山栎类则是海拔２５００米以上硬叶常绿阔叶林及高山灌丛植被的建群种。种的区系成分分析表明：     

FINE STRUCTURE AND COMPOSITION OF THE EGG APPARATUS BEFORE AND AFTER FERTILIZATION IN QUERCUS GAMBELII: THE FUNCTIONAL OVULE

A study of the egg apparatus of Quercus gambelii was made at both the light and the electron microscope levels. This investigation was concerned primarily with the changes that occur in these cells before and after the process of fertilization and what role, if any, is played by the synergids in this phenomenon. The synergids before fertilization are, on the basis of ultrastructure, healthy, intact, functional cells. They have numerous mitochondria, dictyosomes, endoplasmic reticulum, ribosomes, and a typical nucleus. A prominent filiform apparatus is present, but the cell wall only extends a short distance around the micropylar end of the cells. Just before fertilization, one of the synergids degenerates. This is the synergid that receives the pollen tube and its discharge, including both male gametes. Dictyosomes increase in number and activity in the other synergid (persistent synergid) after fertilization. Eventually a complete cell wall forms around both of the synergids. No plasmodesmata are present in these walls. The egg has numerous mitochondria, dictyosomes, endoplasmic reticulum, and ribosomes, both free in the cytoplasm and attached to the endoplasmic reticulum. Lipid bodies are characteristic of this cell. A cell wall is present only around the micropylar end of the egg. After fertilization, little change occurs in the zygote. The number and activity of the dictyosomes increase, apparently in correlation with cell wall formation. The number of lipid bodies increases. The zygote is approximately the same size as the egg. Plastids are scarce, and starch grains are typically absent from all cells of the egg apparatus. It is suggested that the synergids function in the secretion of chemotropic substances that guide the growth of the pollen tube. Comparisons are made between the egg apparatus of Quercus gambelii and that of the other plants studied thus far.     

ASPECTS OF CONE AND OVULE ONTOGENY IN CRYPTOMERIA (TAXODIACEAE)

The axillary complex of female cones of Cryptomeria is initiated as a tangentially extended triangular structure with a rounded apex. It is bilaterally symmetrical. Structures interpreted as prophylls are differentiated first, but they become insignificant in later development. They are succeeded by two successive pairs of lobes, each lobe being the common primordium for an adaxial ovule and a tooth. The ovule initially much exceeds the tooth. The apex of the complex has a diversity of fates and may differentiate as an ovule-tooth pair. A one-to-one relation between teeth and ovules may be lost by abortion of ovules. The initial relation between teeth and ovules is obscured in later development due to extension of tissues at the base of the complex associated with considerable enlargement of the teeth. Histogenesis of the various parts is described, together with the vascular system. There is a vascular supply to the tooth but not the ovule. The results support a direct comparison with the extinct transition conifers Pseudovoltzia and Aethophyllum but do not fully support Florin's generalized model for the arrangement of parts in the axillary complex of conifers.     

A NEW SPECIES OF BLACK OAK (QUERCUS,SUBG. ERYTHROBALANUS,FAGACEAE) FROM THE SIERRA MADRE OCCIDENTAL,MEXICO

Quercus mcvaughii is described as a new species of black oak (subgenus Erythrobalanus) from the Sierra Madre Occidental, in northern Durango and western Chihuahua, Mexico. It is most closely related to the more southern Q. crassifolia. Sessile or subsessile hairs, usually of different sizes, on the abaxial leaf surface distinguish Q. mcvaughii from Q. crassifolia, where hairs are similar in size and conspicuously stipitate. A key is provided for distinguishing similar species in the region. Intergradation of Q. mcvaughii with Q. crassifolia, Q. hypoleucoides, and Q. sideroxyla is reported.     

中国壳斗科栎亚科花粉形态研究

本文应用光学显微镜与扫描电子显微镜观察了壳斗科所属栎亚科2属26种2变种的花粉形态,并以本科其它属一些代表种作对比,试图从孢粉学方面为栎亚科的系统分类提供依据。 花粉外壁纹饰在扫描电镜下可分三种类型,即水青冈型(含水青冈属),栎型(含栎属和三棱栎属),栗型(含栗属、锥属和柯属),花粉的类型与植物形态分类的三个亚科一致。 栎亚科的花粉外壁纹饰在扫描电镜下为颗粒聚集成的种种形状。栎属可区分为四种类型,即颗粒状、颗粒——蠕虫状、聚颗粒及芽孢状,其中类型一、二、三为常绿种类,类型四为落叶种类。花粉纹饰在常绿与落叶种类之间有较明显的差异,而青冈亚属和栎亚属之间却没有界线。因此,栎属仍以包含两个亚属为宜。三棱栎属花粉纹饰则介于栎属的类型二与三之间。     

SOME HISTOCHEMICAL,ULTRASTRUCTURAL, AND NUTRITIONAL ASPECTS OF THE OVULE OF QUERCUS GAMBELII

Histochemical analyses of the ovule of Quercus gambelii show that the major food reserves (starch grains and lipids) are located almost exclusively within the outer integument. Vascular traces are present only within this integument which contains numerous, well-developed plasmodesmata. The inner integument is virtually devoid of any food reserves and has very few plasmodesmata. The ovule has a persistent chalazal extension of residual nucellar cells (called the postament) which projects into the embryo sac. Due to the above information and the fact that the synergids rarely contain starch and no plasmodesmata are present in the walls of any of the cells of the egg apparatus (Mogensen, 1972), it is concluded that the synergids play little or no role in embryo sac nutrition. Rather, it is proposed that the pathway of available food materials in the young ovule is from the outer integument to the chalaza and through the postament into the embryo sac.     

SPATIAL DISTRIBUTION AND DEVELOPMENT OF ROOT SPROUTS IN FAGUS GRANDIFOLIA (FAGACEAE)

Root sprouts around 31 Fagus grandifolia parent trees, some declining due to beech bark disease, were studied to describe the pattern of sprout distribution, the ecological importance of this pattern, and the relationship between sprout patterns and parent vigor. Microtome sections of roots were studied to determine the histological origin of sprouts. Sprout distribution was circular and usually centered on the parent tree. Most sprouts were within 8 m of the parent and remained attached to the parent root system even after the sprouts reached 10 yrs of age. Root sprouting in F. grandifolia may be effective in replacing dead parent trees, but the potential for clones to spread is limited. Spatial distribution of sprouts was mostly unaffected by tree vigor. Root sprouts originated from callus tissues associated with wounds on superficial woody roots.     

SYNCOTYLY IN QUERCUS ARIZONICA

An investigation was made concerning the gross morphology and the internal anatomy of Quercus arizonica embryos. It was found that the percentage of fused- and separate-cotyledoned embryos varies from tree to tree. Fusion of the cotyledons is congenital. Intermediate stages of fusion occur. The vascular pattern is the same in both fused- and separate-cotyledoned embryos. The number of cotyledonary traces varies in both types of embryos. The relationship of the single-cotyledoned embryo of Quercus to the origin of monocotyly is discussed.     

UNDERGROUND SYSTEMS OF GAMBEL OAK (QUERCUS GAMBELII) IN CENTRAL UTAH

Excavation to a depth of 1 m of a 3 × 4 m portion of a clone of Quercos gambelii revealed the presence of a massive underground system of lignotubers, interconnecting rhizomes and roots. Lignotubers comprised the greatest proportion (72%) of the total below ground biomass (81 t/ha). Lignotubers are distinctive in appearance: they are an enlarged stemlike structure with numerous clusters of adventitious buds on the surface. Anatomically, they are comparable to the above ground stems with growth rings. Lignotubers are lobed and distorted, giving the appearance of a burl. Rhizomes are round to I-beam in shape with a star-shaped pith, distinct annual rings, bud traces, and branch gaps. There were also clusters of adventitious buds on rhizomes, although not as dense as those on the lignotubers. Roots are oval in cross section with discernible growth rings, no pith, and no bud traces.