BIFURCATION OF THE STEM APEX IN ASCLEPIAS SYRIACA

In Asclepias syriaca the overall inflorescence is an anthoclad in which the peduncles are non-axillary, each occurring about 60° away from the axil of a leaf. Ontogenetically, a peduncle is initiated when the stem apex expands laterally and bifurcates into separate apices, neither of which is subtended by any type of organ. One of the two apices continues as the functional apex of the stem (bifurcating again at each subsequent node), and the other functions as the apex of the peduncle. The peduncle first produces a bract and, then, a pedicel in the axil of the bract. Subsequent pedicels are each axillary to separate bracts. The pedicels, therefore, can be interpreted as ordinary lateral branches. However, because the bifurcations of the stem apex are not associated with subtending organs, the branching of the stem does not conform to expected monopodial or sympodial systems in the angiosperms. This suggests the possibility that each bifurcation of the stem apex is a true dichotomy. The anthoclad axis, thus, is a series of dichotomies. Although such a series may have been phylogenetically derived from a monopodial or sympodial ancestor, it is also possible that it may have been retained from a primitive, dichotomizing inflorescence.     

ULTRASTRUCTURE OF DEVELOPING AND MATURE NONARTICULATED LATICIFERS IN THE MILKWEED ASCLEPIAS SYRIACA L. (ASCLEPIADACEAE)

The ultrastructure of developing and mature nonarticulated laticifers in Asclepias syriaca L. (the common milkweed) was studied by conventional fixation and staining techniques and by osmium impregnation techniques. The mature laticifer protoplast in A. syriaca possesses a large central vacuole with an intact vacuolar membrane. Formation of this vacuole apparently results from dilation and subsequent enlargement of endoplasmic reticulum and possibly in part by fusion of smaller vacuoles and limited cellular-lytic autophagy. Widespread digestion or autophagy of cytoplasm within vacuoles is not evident. Nuclei, mitochondria, dictyosomes, and small vesicles are the most prominent components distributed in the peripheral cytoplasm. Plastids appear to degenerate as the laticifer matures. The specialized cellular component, latex, which is the vacuolar content of the laticifer, is interpreted to be produced in the cytoplasm and subsequently incorporated into the large central vacuole. Rubber globules, the most prominent latex component, are surrounded by a membrane that does not have a trilaminate structure. Globules are associated with an electron-dense fibrillar component in the vacuole.     

ULTRASTRUCTURE OF NON-ARTICULATED LATICIFERS IN MATURE EMBRYOS AND SEEDLINGS OF ASCLEPIAS SYRIACA L. (ASCLEPIADACEAE)

The protoplast of the non-articulated branched laticifer in the embryo and seedling of Asclepias syriaca L. was studied at the ultrastructural level and was found to differ from that of adjacent cell types. Embryonal laticifers possess numerous vesicles with electron-dense contents, but lack a large organized central vacuole. Plastids have few lamellae, possess phytoferritin, and accumulate small amounts of starch. Other organelles and membrane systems are similar to those in other cells. After germination, laticifers develop numerous elongated vacuoles by dilation of endoplasmic reticulum. Nuclei in laticifers within the hypocotyl of seedlings are highly lobed and possess dilated perinuclear spaces. Plastids and other organelles are similar to those observed in the protoplast of laticifers in the embryo. The latex or rubber component of the laticifer is not apparent in mature embryos of 72-hr seedlings.     

镉在黑藻叶细胞中的亚显微定位分布及毒害效应分析

水生植物被认为能积累和浓缩重金属,本文以不同浓度Cd培养7天的黑藻为材料,研究了Cd的积累,亚细胞分布,亚显微定位,存在形态及对矿质营养吸收,光合速率和呼吸速率的影响,以揭示Cd的植物毒害机理.研究结果表明,随培养液中Cd浓度的增加,植株体内的Cd含量显著上升,富集系数为193-307;不同亚细胞组份中的Cd含量也都呈上升趋势,但分布显著不均,分配顺序依次为细胞壁＞可溶性部分＞细胞器,其中,积累在细胞壁中的含量所占比例呈下降趋势(61.66%-52.00%),而可溶性部分中则递增,细胞器部分结合的Cd含量所占比例相对恒定;硫化物-银法定位结果直观显示出Cd分布在细胞壁、叶绿体、细胞核和液泡中;逐步提取法分析表明受Cd毒害的黑藻体内Cd以不同化学形态存在,其中NaCl提取态占比例最大(55.05%),其他则较少,依次为FNaCl＞FHAc＞FWater＞FEthanol＞FHCl＞FResidue;Cd对黑藻的营养元素吸收也产生影响,主要是促进对Ca,Mn,Cu,Fe的吸收,降低对大量元素P,K的吸收;Cd对黑藻的光合速率和呼吸速率都有较强的抑制作用.结果表明Cd毒害与处理浓度间存在显著的剂量-效应关系;亚细胞分布与对细胞超微结构的损伤关系密切;Cd破坏了黑藻正常生理活动的结构基础和离子平衡,并造成功能紊乱.这些都是Cd对植物产生毒害的重要原因.     

FLORAL POLYMORPHY AND AMPHIMICTIC BREEDING SYSTEMS IN RUELLIA CAROLINIENSIS (ACANTHACEAE)

The taxonomically complex eastern U. S. species R. caroliniensis produces six functional or partially functional floral morphs. They are chasmogenes, reduced chasmogenes, morphologic protogynous chasmogenes, multistylous chasmogenes, cleistogenes, and semi-cleistogenes. The plants are uniformly self-compatible and generally produce normal fruits and seeds. The species has the morphological basis of a nearly balanced breeding system between allogamous and autogamous reproduction. Observations and comparisons on garden and greenhouse cultures suggest that R. caroliniensis is a seasonal cleistogamic species, and it is proposed that the different breeding systems are the chief causes of the difficult taxonomic problem in the species.     

EFFECTS OF VARIATION IN FLORAL MORPHOLOGY ON POLLINATION MECHANISMS IN ASCLEPIAS TUBEROSA L., BUTTERFLYWEED (ASCLEPIADACEAE)

Field observations revealed the presence of fruit-producing (fruiting) and non-fruit-producing (non-fruiting) plants in two south central Oklahoma populations of Asclepias tuberosa L. Comparative measurements of floral characteristics between fruiting and non-fruiting plants indicated that fruiting plants have significantly larger alar fissure widths and a greater percentage of intact pollinaria. The smaller alar fissure width on flowers of non-fruiting plants apparently reduces the probability of successful pollinia insertions in these plants. Greater numbers of observed pollinia insertions into fruiting-plant fissures appear to be the result of the increased likelihood that pollinia, which are significantly narrower than the fissures of fruiting plants, will be inserted into fruiting-plant fissures than those of non-fruiting plants. Apparently non-fruiting plants act primarily as pollinia donors while fruiting plants act primarily as pollinia recipients. These characteristics of butterflyweed tend to promote a dimorphic, allogamous type of pollination.     

BREEDING SUCCESS AND POPULATION GROWTH IN A COLONY OF HERRING AND LESSER BLACK-BACKED GULLS LARUS ARGENTATUS AND L. FUSCUS

This paper describes the results of investigations into the factors affecting breeding success of the Herring and Lesser Black-backed Gulls Larus argentatus and L. fuscus, in the large colony on Walney Island, northwest Lancashire, between 1962 and 1965. These investigations were concerned with the incubation period, and the first ten days after hatching. The survival of chicks to ten days is 67% in Herring Gulls, and 56% in Lesser Black-backs. Most of these losses occur in the period just after hatching and are due to “cannibalism” by other gulls. This form of predation does not appear to be masking any effects from starvation or disease. The following factors contribute to egg or chick mortality:breeding too late (and, to a much smaller extent, too early); breeding in the open, as opposed to amongst cover; the facts that eggs in small clutches have a lower hatching success than those in large ones and that Herring Gull (but not Lesser Black-back) chicks in small broods are less likely to survive to ten days than are those in large broods. Chick mortality after the first ten days is not certainly known. About 30% of the eggs laid gave rise to fledged young— or about one fledged chick per pair. In the Herring Gull, the average clutch size (2.56) is lower than that of the Lesser Black-back (2.76). Both species show a seasonal decline in clutch size—this occurs earlier in the Herring Gulls than in the Lesser Black-backs. The Walney population, which stood at about 700 pairs in 1950, had reached 12,000 in 1957, and is at present about 18–19,000 pairs. It is suggested that this increase may be linked to the greater availability, or exploitation, of human garbage in the Morecambe Bay area. The population explosion between 1950 and 1957 must have been partly due to massive immigration and could not have come about through natural increase alone. The possible influences of the gulls' behaviour on the population growth are discussed. There is no evidence of any “shock disease”, although the Walney colony is very crowded. “Cannibalism” is regarded, not as evidence of a failing food supply, but as an extension of the normal hunting behaviour of these omnivorous gulls; it will be an economical means of obtaining food only in a large, dense colony, such as Walney. It may be offset by increased breeding efficiency due to social factors.     

PECTINASE IN ASCLEPIAS LATEX AND ITS POSSIBLE ROLE IN LATICIFER GROWTH AND DEVELOPMENT

A pectinase with a pH optimum of 5.2 is present in the latex of the common milkweed, Asclepias syriaca L. The enzyme was partially purified from the serum fraction of fresh latex by dialysis and ammonium sulfate fractionation. Enzyme activity was detected by a viscometry assay and by the dinitrosalicylic acid assay for reducing sugars. Pectin and polygalacturonic acid could serve as substrates for the enzyme. Pectolytic activity in latex presents a basis for describing the development of the non-articulated branched laticifer system. Enzyme activity may facilitate intrusive tip growth of the laticifer among other cells by solubilizing pectic substances of the middle lamella and also may be important for loosening wall material of the laticifer itself to facilitate extension growth.     

BREEDING SYSTEMS AND FECUNDITY IN THE AMERICAN GINSENG,PANAX QUINQUEFOLIUM (ARALIACEAE)

American ginseng is self-compatible with fecundity among bagged inflorescences equivalent to (Missouri) or greater (New York) than that observed for nonbagged inflorescences. Population differences in flowering time and synchrony, protandry, autogamy, xenogamy, and fecundity, imply major genetic divergence in the species.