共查询到20条相似文献,搜索用时 0 毫秒
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A total of 764 breeding soundness examinations was conducted on beef bulls utilizing the method of examination and criteria for classifying bulls of the Society for Theriogenology. In addition to this examination each bull was subjected to scrotal circumference measurement and to weighing. Classification of the bulls according to breeding soundness potentials was as follows: 88% of the bulls were satisfactory potential breeders, 8% of the bulls were questionable potential breeders and 4% of the bulls were unsatisfactory potential breeders. The proportions of bulls in each classification; satisfactory, questionable, or unsatisfactory; were not different among the four breeds evaluated. The majority of bulls evaluated in this study were between 14 and 36 months of age and weighed between 900 and 1500 pounds. For the ages and weights evaluated, scrotal circumference measurement variances were not closely related to age and weight differences. There was a tendency shown for “Questionable” and “Unsatisfactory Potential Breeders” to have smaller scrotal circumference measurements. The study indicates that Angus, Charolais, Horned Hereford and Polled Hereford bulls of breeding ages and weights should have scrotal circumference measurements of at least 32 centimeters in order to be classified as “Satisfactory Potential Breeders”. 相似文献
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The morphology of the stomatal complex in Pinus strobus L. and P. banksiana Lamb, is described and it is proposed that the stomatal complex should be considered an eight-celled complex consisting of two guard cells, and two polar, two lateral, and two hypodermal subsidiary cells. An ontogenetic study found these cells closely related developmentally. It was also found that the stomatal complex in these two pines could not readily be classified as haplocheilic because a polar subsidiary cell arises from the same protodermal cell as does the guard cell mother cell. A modification of the classical concept of stomatal development was necessary to describe the stomata as eumesoperigenous. 相似文献
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滇产云南松、思茅松松针油的化学成分 总被引:7,自引:0,他引:7
云南松(Pinus yunnanensis Fr.)和思茅松〔Pinus kesiya Royle ex Gord.var.langbianensis(A.Chev.)Gaussen〕为云南针叶林主要树种。我们已研究了思茅松松节油的化学成分,为松针油利用提供科学数据,比较松节油与松针油化学成分的同异,并考察α-蒎烯,β-蒎烯的含量与分布的关系,本文用气相色谱/质谱/计算机联用仪,对滇南到滇中水平分布及由低到高垂直分布的八个云南松和九个思茅松松针油油样进行了定性、定量分析。 相似文献
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Coleman R. Robison 《American journal of botany》1977,64(6):726-732
Dwarf shoots and needle leaves of Pinus triphylla Hollick and Jeffrey and P. quinquefolia Hollick and Jeffrey have been discovered recently in a Late Cretaceous age clay deposit on Martha's Vineyard Island, Massachusetts. Detailed study of these fossils provides further information on the internal construction of the two taxa. This new information permits both species to be compared easily with similar fossil forms from the Upper Cretaceous of Japan as well as with dwarf shoots and needles of modern species of Pinus. As a result, the relationships between Cretaceous pines and the extinct genus Prepinus are found to be less than previously believed. Moreover, the dwarf shoots and needles of Cretaceous members of the genus Pinus appear to be most like those of present-day species included in the subgenus Pinus. 相似文献
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云南东南部松属植物分布的特点 总被引:1,自引:0,他引:1
本文从云南东南部松属植物的种类入手,探讨了其生态特性及分布特点。通过分析可以看出由各个方向分布而来的松属各种在此都趋向于其分布的边界,使得本区成为松属植物中不同区系成分分布的一个限制地域,并就产生这种特殊分布的原因进行了探讨;进一步从松属植物分类上分析了国产松属性状状态及其组合的分布,继此又对我国各地区所产松属植物与西南地区进行了比较,得出了云南东南部是我国松属植物发育较好和多样化的一个地区。此外,还分析了本区松属的特有种和替代种。并提出了大明松与黄山松的区别点属黄山松的变异范围之内,应予归并。 相似文献
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马尾松人工林种群自然稀疏模型的研究 总被引:3,自引:0,他引:3
在福建北部丘陵山区生长发育正常的各种类型的马尾松人工林中,设置固定样地,测算胸径、株高、优势高、株数、蓄积量、年龄等数据,以植物种群生物量增长模型dB/dt=rB[1-(B/K)^θ]和3/2自疏法则为理论依据,出森林自然稀疏过程密度变化规律的模型:N={[A(1 ce^-ft)^b]^-p-[A(1 ce^-ft0)^b]^-p No^-p}^-1/p,该模型适用于描述各种密度林分的自然稀疏规律。经用闽北马尾松人工林固定样地资料验证,证明此模型能很好地拟合实际的密度观察资料,显示了较高的准确性和较大的适用性,有良好的使用价值。 相似文献
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广西松属一新种 总被引:1,自引:0,他引:1
<正> 拉雅松 新种 图1 Pinus crassicorticea Y. G. Zhong et K. X. Huang, sp. nov. (subgen. Pinus; Sect. Pinus). Species affinis P. massonianae, sed cortice multo crassiore, foliis rigiioribus; canalibus resiniferis 8—13, marginalibus et prope fascicule vasorum positis; ramulis glaueis; squamis strobili hornotini apice 3-spinulosis differt. Arbor 18—35 na alta, trunco ad 60—90 cm; cortex persistens, intense 相似文献
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马尾松高效再生体系的建立(简报) 总被引:2,自引:0,他引:2
利用组织培养技术快速繁殖针叶树,不仅为植树造林所需大量苗木开辟了一条快速高效的新途径,是生产优良无性系的捷径,而且也是植物基因工程技术应用于针叶树品种改良的前提条件。它将在林木种苗产业化和林木良种化进程中发挥重要作用。针叶树的离体培养和植株再生一直是植物组织培养研究中难度较大的一个领域。近几十年来,随着世界各国对发展无性系育林业的日益重视,针叶树组织培养研究取得了很大的进展[1-3]。马尾松(Pinus massoniana Lamb.)是我国南方主要的造林及绿化树种,其木材和松脂具有重要的经济价值。然而在生产实践中,种子园种子… 相似文献
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Mature needles and elongating current year's needles of Pinus strobus growing in Massachusetts and P. brutia growing in Israel were collected monthly or bimonthly for seasonal analysis of leaf cambial activity. Mature needles produced secondary phloem but no xylem, and, regardless of the season, had a cambial zone from 2 to 3 cell layers wide. In the current year's needles maturation was basipetal and the procambium differentiated into primary xylem, primary phloem, and the phloem-producing vascular cambium before needle maturity. One- and 2-year-old needles of Pinus strobus produced slightly over 4 cell layers of phloem between April 15 and September 1 of 1983, with a peak production rate of about 2 cell layers per month in May and early June. One-year-old needles of P. brutia produced about 6 phloem cell layers in 1983, with phloem being produced throughout the year except in midsummer. This was contrasted by fall and winter dormancy in needles of P. strobus. 相似文献
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HEARTWOOD FORMATION IN PINUS RADIATA (D.DON.) 总被引:1,自引:1,他引:0
《The New phytologist》1954,53(3):517-524
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对缙云山亚热带常绿阔叶林不同演替阶段马尾松(Pinus massoniana)种群生殖器官的生物量配置进行了系统研究。结果显示从蕾期、花期到果熟期,马尾松种群生殖器官的生物量配置逐渐增加,但不同演替阶段的生殖配置格局各异。马尾松纯林各生殖阶段的生殖配置分别为1.31%,7.61%,23.25%;针阔混交林各生殖阶段的生殖配置分别为0.6%,3.29%,15.14%;林缘旷地各生殖阶段的生殖配置分别为0.76%,3.78%,18.44%。一年中缙云山马尾松种群的生殖配置动态变化呈现低一渐高一高一低的规律性。缙云山马尾松种群的生殖年龄大致可分为4个时期,即幼龄生殖期、过渡生殖期、稳定生殖期和衰退生殖期。种群密度和群落透光度与其生殖配置显著相关。 相似文献
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黑松花粉个体发育的研究 总被引:10,自引:0,他引:10
黑松(Pinus thunbergii Parl.)小孢子发生在三月上、中旬,三月下旬至四月上旬为花粉发育期,散粉时花粉为四细胞型。减数分裂后期Ⅰ、Ⅱ淀粉粒聚集于赤道区。花粉分裂前,细胞质浓缩至远极面,核由松散结构转变为紧密的球状结构。胼胝质最初出现在紧靠母细胞壁的内侧,然后分别出现在后期Ⅰ、Ⅱ的赤道区紧靠母细胞壁。有时,减数分裂的后期Ⅰ、Ⅱ不形成胼胝质或胼胝质发育不完全,在子核之间不产生细胞壁。黑松具单、三个或四个气囊的异型花粉。 相似文献