Secondary phloem anatomy of Cycadeoidea (Bennettitales)

Secondary phloem anatomy of several species of Cycadeoidea is described from trunks in the Wieland Collection, Peabody Museum of Natural History. The trunks were collected from the Lakota Formation, Lower Cretaceous, Black Hills of South Dakota. Secondary phloem is extensively developed and consists of alternating, tangential bands of fibers and sieve elements, with rare phloem parenchyma. Uniseriate rays, 2-22 cells high, occur between every one to three files of the axial system. Fibers are long, more than 1200 μm, approximately 26.6-34.2 μm in diameter, and have slit-like apertures on the lateral walls. Sieve elements range from 16-25 μm in diameter and are up to 500 μm long. Elliptical sieve areas appear on both end and radial walls and measure 10 μm across; minute spots, which may represent sieve pores, are present within the sieve areas. Secondary phloem of North American Cycadeoidea is similar in organization (alternating tangential bands) and cell types (sieve cells, fibers, axial parenchyma) to that known in other extant and fossil cycadophytes and some seed ferns. The unusual pattern of cell types and thickness of secondary phloem is discussed in the context of plant habit, phloem efficiency, and potential phylogenetic importance.     

Diversity variation and tempo-spatial distribution of Otozamites (Bennettitales) in the Mesozoic of China

Otozamites is a representative fossil leaf morphogenus of the extinct Bennettitales, with an extensive distribution during the Mesozoic, especially in China. Understanding the fossil diversity variation and distribution pattern of Otozamites in China will provide information on biodiversity of bennettitalean plants as well as for reconstruction of palaeogeography and palaeoclimate conditions during the Mesozoic. So far, 46 species of this genus have been described in China, excluding unspecified species. The results show that the fossils of Otozamites are extensively recorded in the Late Triassic, and then reach their maximum development in the Early Jurassic, followed by a reduction in diversity in the Middle and Late Jurassic, and finally become extinct at the end of Early Cretaceous. Geographically, they occur in both Northern and Southern Floristic Provinces in the Mesozoic of China, with a relatively higher abundance in the Southern Floristic Province. It implies that the diversity variation and distribution of Otozamites are closely related to the change of the palaeoclimatic conditions. The warm and humid climate prevailed in the Late Triassic and Early Jurassic in South China, propitious to the development of Otozamites. After the Middle Jurassic, dry and hot climate may have caused the lower diversity level and blocked the development of Otozamites; finally at the end of the Early Cretaceous, the frequent arid climate may be a major cause for the extinction of Otozamites.     

Bennettitales from the Grisethorpe Bed (Middle Jurassic) at Cayton Bay, Yorkshire, UK

Middle Jurassic fossil plants from the Grisethorpe Bed at Cayton Bay and Grisethorpe Bay, Yorkshire, UK, are preserved in a soft claystone, and plant mesofossils recovered by sieving reveal excellent details of external structure. Studies of these mesofossils complement previous work on macrofossils from the Grisethorpe Bed and allow the plant fossils in this classic flora to be studied in a similar way to those preserved in Cretaceous mesofloras. Bennettitales, a key group in discussions of how angiosperms may be related to other seed plants, are especially well represented among mesofossils from the Grisethorpe Bed. Abundant bennettitalean leaves, scale leaves, and fragments of pollen and ovulate organs provide new information on these extinct plants. In particular, a specimen of Williamsoniella coronata (presumed aborted) shows only weak differentiation between interseminal scales and ovules and provides further evidence of homology between these structures.     

Formation of the Micropyle in Tilapia mossambica Peters and Stigmatogobius javanicus (Blkr.)

The formation of the micropyle in Tilapia mossambica and Stigmatogobius javanicus, two fresh water teleosts is described. In T. mossambica the micropyle is formed by a single modified follicular cell, while in S. javanicus it is formed by a cellular mass derived from the follicle.     

The Induction of Root Dormancy in Picea sitchensis (Bong.) Carr. by Abscisic Acid

Abscisic acid at 10⁴ M inhibited elongation and induced dormancyin roots of Sitka spruce cuttings growing in solution culture.The dormancy was characterized by superficial browning whichprogressed towards the root tip and by the development of alayer of lignified and suberized cells around the root apex.The dormant roots remained alive and resumed growth on transferto ABA-free solutions. The induction of dormancy was confinedto those roots actually bathed in the ABA solution and a rangeof conditions which affected shoot activity did not alter theresponse. By contrast, the time for which the roots had beenelongating strongly influenced root dormancy since it was notinduced in roots which had recently begun to elongate in solutionculture. The possible role of ABA in inducing root dormancyunder adverse conditions is discussed.     

黄檗（芸香科）的珠孔塞和珠孔的形态发育及花粉管在子房室中的生长路径

利用扫描电子显微镜术和光学显微镜术研究了黄檗(Phellodendron　amurense　Rupr.)的珠孔塞和珠孔的形态发育和花粉管在雌蕊中的路径。黄檗胚珠的珠孔塞起源于珠柄。随着胚珠生长,珠孔塞逐渐增大,胚珠成熟时珠孔塞变得相当大并紧密地覆盖在珠孔上。当雌花进入可传粉期时,珠孔塞的形态发生很大变化,其表面细胞径向延伸,形成柱形、半乳突或乳突细胞。受精后,珠孔塞体积变小并逐步退化。花粉管在子房室中并非一定经过珠孔塞结构。花粉管是否经过珠孔塞取决于它们进入子房室的位置。我们不支持先前研究者关于珠孔塞主要充当对花粉管生长的机械作用的观点。我们对黄檗胚珠的珠孔的形态发育研究显示,在不同的生殖时期,珠孔的结构会发生变化,在传粉时期它的结构显示不对称性。黄檗珠孔塞和珠孔的发育与雌配子体发育存在密切关系。     

Diurnal water storage in the stems of Picea sitchensis (Bong.) Carr.

Abstract. Two models of the relationship between diurnal variation in shoot water potential and transpiration in 14-year-old Picea sitchensis (Bong.) Carr. were compared. The first model was a physiologically based resistance-capacitance (R-C) analogue with its associated differential equations. The second was a non-physiological discrete-difference (D-D) or stochastic transfer function model. The RC model included only the effect of water storage in the phloem and bark while the D-D model implicity included all storage mechanisms. The R-C and D-D models explained similar fractions (62% and 68% respectively) of the variation in shoot water potential due to diurnal changes in transpiration rate. However, the D-D model had fewer parameters than the R-C model. The results from the D-D model showed that the resistance to flow from soil to shoots along the trunk, (RT), was 5 × 10³ MPa kg^-1s and the capacitance of the phloem and bark treated as a single store, (C_s), was 1.6 kg MPa^-1. It is suggested that the resistance to flow into storage (R_s) is much greater than R_T and can be disregarded. A non-linear version of the D-D model suggested [hat resistance to flow in the trunk increases with increasing transpiration rate.     

Una nueva especie de Weltrichia (Bennettitales) del Jurásico Medio de la Formación Tecomazuchil (Oaxaca, México)

A new species of Weltrichia (Williamsoniaceae: Bennettitales) is described from the Middle Jurassic of Oaxaca. The specimens come from the Tecomazuchil Formation in the Ayuquila region, at the border between the Oaxaca and Puebla states. Fossils are preserved as impressions and compressions, in a fine-grained sublitharenite sequence deposited in a fluvial environment. Preserved diagnostic characters include: large size; a cup-shaped receptacle showing seven radially arranged and basically fused microsporophylls bearing synangia. Microsporophylls are ornamented with longitudinal striations and fine brittled hairs on the edge of their wide base, and taper into a narrow distal tip. In the adaxial part of the microsporophylls seven to nine synangia are observed. These characters differentiate the new species Weltrichia mixtequensis from all previously recorded species from Mexico or elsewhere. The presence of this new species in the Middle Jurassic strata of the Ayuquila region add to the scarce fossil record of microsporangiate structures in the Jurassic flora of Mexico.     

An Unusual Method of Formation of Micropyle in the Oocytes of a Gobiid Fish Oligolepis acutipennis (Cuv. & Val.)

The formation of the micropyle in the oocytes of a gobiid fish O. acutipennis is described. In O. acutipennis the micropyle is formed at the summit of a cone termed here as the “micropylar cone”. A single follicular cell takes part in the formation of the micropyle while the two cells on either side seems to play a supporting role in the process.     

Substrate Availability in Relation to Daylength Effects on Tracheid Development in Picea sitchensis (Bong) Carr

Changes in assimilation and growth were studied in Picea sitchensis(Bong) Carr. seedlings initially grown in long days and subsequentlytransferred to short days. These results, and some from a supplementarystudy involving transfer to reduced light quantity alone, wereexamined in relation to tracheid development. Increases in photosynthesis conditioned by reduced daylengthwere greater in magnitude than those resulting from a reductionin light quantity alone. Possible reasons for this as well asthe apparent absence of such photoperiodic effects in the fieldare discussed. Following a reduction in daylength, ¹⁴C incorporation into reservesand new growth generally decreased while turnover materialsincreased in prominence. Some local changes in this generalpattern were apparent, these changes being consistent with growthchanges in the organs under consideration. Initial changes in tracheid wall thickness and diameter aftershort-day transfer appear to be correlated with expected andobserved changes in endogenous substrate, the results for tracheiddiameter confirming a previous observation that substrate levelexerts an important modifying influence on tracheid radial expansion.     

Somatic embryogenesis in Sitka spruce (Picea sitchensis (Bong.) Carr.)

Embryonal-suspensor masses from immature embryos from cones of Sitka spruce (Picea sitchensis (Bong.) Carr.) proliferated on a modified Murashige & Skoog medium with N⁶-benzyl-aminopurine, kinetin, 2,4-dichlorophenoxyacetic acid and an organic nitrogen source. The slimy white embryonal-suspensor masses with proembryos were maintained on a solid proliferation medium with reduced amounts of growth regulators. Transfer of embryonal-suspensor masses to a non-woven polyester carrier with liquid maturation media containing ±2-cis-4-trans-abscisic acid and a reduced amount of inositol and organic nitrogen resulted in synchronized embryo formation. Further development was achieved on a medium without ±2-cis-4-trans-abscisic acid and organic nitrogen. Somatic embryos were successfully transferred ex vitrum.Abbreviations ABA ±2-cis-4-trans-abscisic acid - BAP N⁶-benzyl-aminopurine - ESM embryonal-suspensor masses - KIN kinetin - 2,4-D 2,4-dichlorophenoxyacetic acid     

Development of a set of highly polymorphic genomic microsatellites (gSSRs) in Sitka spruce (Picea sitchensis (Bong.) Carr.)

Robust, polymorphic microsatellite DNA markers (simple sequence repeats—SSRs) are valuable tools for a range of tree conservation and breeding applications. SSRs are routinely used in the study of population genetic structure and diversity, pedigree reconstruction and genetic linkage mapping. Their abundance in the genome, co-dominant inheritance and potential for cross-species amplification make microsatellites highly prized markers. This paper characterises 22 novel genomic polymorphic microsatellite loci for Sitka spruce (Picea sitchensis (Bong.) Carr.). Amplification of DNA from Sitka spruce material was carried out both with a set of unrelated trees to obtain diversity statistics for each locus, and with the progeny of a full-sib family to test simple Mendelian inheritance. Observed heterozygosity ranged from 0.38 to 0.91 and allele number per locus ranged from 6 to 21, with a mean of 12.2. In addition, the primer pairs were tested with DNA from Norway spruce (P. abies) and white spruce (P. glauca) to investigate their potential for cross-species amplification and ten loci amplified in all three species. The results from these genomic microsatellites are compared to data generated from microsatellites derived from Picea EST libraries. In summary, this novel, highly polymorphic markers represent a significant addition to the rapidly expanding Picea genomics tool-box. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Intraspecific variation of DNA per cell between Picea sitchensis (Bong.) Carr. provenances

Quantitative intraspecific variation of DNA per cell was established by means of biochemical, double wavelength microspectrophotometry and micro-densitometric analyses of root tips from 7 seed sources of Picea sitchensis (Bong.) Carr. Northern seed sources possessed more DNA per cell than southern provenances. This, perhaps, is an indication of DNA adaptability through plasticity resulting from changing environmental stress over the natural range.     

The Kinetics of Tracheid Development in Tsuga canadensis Carr. and its Relation to Tree Vigour

Cell counts from samples taken at weekly intervals, from 14May to 22 October 1969, in a T. canadensis stand in Massachusetts,U.S.A., showed that the width of the annual ring was correlatedwith the rate of cell production and that only the least vigoroustrees (c. 20 tracheids year^–1) had a shorter growing season.The time required for completion of a cell-division cycle inthe cambial zone decreased during the course of the season,from 35 to 20 days for the less vigorous trees (25–45tracheids year^–1) and from 28 to 10 days for the morevigorous trees (45–100 tracheids year^–1). The timerequired for the completion of radial growth of the tracheidsdecreased from 18 to 9 days, with no evidence of any changeswith tree vigour. The actual radial growth-rate of the tracheidswas constant within the range 1.5–3 um day^–1. Thetime required for deposition of the secondary cell wall increasedfrom 10 to 50 days, with little evidence of any changes withtree vigour. The actual rate of deposition of cell wall materialwas about 0.15 µ² µ^–1 day^–1 and seemedto show little change during the course of the season. The timeperiod required for lysis of the cytoplasm was about 4 days,with no evidence of any changes with tree vigour and littleevidence of any changes during the course of the season.