摘要:

This investigation begins with the late zygote and traces ultrastructural development to the late globular stage of the embryo. Two nucleoli and satellite nucleoli sometimes occur in the zygote nucleus. Mitochondria, dictyosomes, cytoplasmic ribosomes, rough ER, and lipid bodies are numerous in the zygote. Microbodies are occasionally seen. The cell wall becomes well developed before the first division. No plasmodesmata occur in the zygote wall. The basal cell of the proembryo and the suspensor cells of the later embryo have very dense cytoplasm with a high concentration of cytoplasmic ribosomes. The nuclei are very electron opaque. The terminal cell and the cells of the embryo proper have a fine structure similar to that of the zygote. Plastids increase in number, size, starch content, and amount of thylakoid lamellae as the embryo develops. Mitochondria are numerous and appear active at all stages. Dictyosome activity, ribosomal aggregation, and the amount of ER are highest during the late globular stage. Lipid bodies are present up to the early globular stage, then disappear. The inner cell walls of the embryo are thin and have many plasmodesmata. These walls begin to thicken at the late globular stage, and at this time the size of the embryo begins to show an increase over that of the zygote. The results show a corresponding increase in the amount and activity of the metabolic machinery as the development of the embryo progresses. Lipids are probably more important as a nutrient source in the zygote and early embryo; starch becomes more important in the late stages. Absorption of nutrient material into the embryo sac and developing embryo appears to be from the chalazal end.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14043.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

In order to assess the validity of various interpretations of tubular leaves of angiosperms, a histogenetic study of the ontogeny of adult leaves ofDarlingtonia californicawas undertaken. The adult leaf ofDarlingtoniais characterized by a sheathing leaf base, an elongate ascidium, an overarching hood, and two “fishtail” appendages which arise near the leaf apex. A keellike growth, with two rows of alternate vascular bundles, traverses the tube from base to mouth. Ontogenetic studies show that the primordium arises by a monopodial rather than a sympodial mode of growth as previously reported. After the formation of a small, erect primordium, a restricted adaxial meristem is initiated that expands both adaxially and upwards. This “querzone” serves, in effect, to congenitally combine the two primordial margins during its extension. Growth and maturation of the subjacent portions cause tubular elongation in the leaf. Primordial apical divisions are later replaced by more general intercalary growth with acropetal and centrifugal maturation. The hood and fishtails are established early in ontogeny by adaxial growth of the primordial apex and subsequent activation of juxtaposed localized meristems. Comparative morphology has established that the epiascidiate leaf is a foliar appendage that undergoes certain specific morphogenetic modifications. It has a structural relationship to ensiform appendages ofAcaciaandAcorusas well as to peltate foliar organs. The early ontogeny ofDarlingtonialeaves is considered to be homologous with other epiascidiate foliar organs, including some supposedly primitive carpels.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14044.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

The genusKermadecia(Proteaceae), originally described as endemic to New Caledonia, has been expanded in recent decades to include three species from the New Hebrides and Fiji. Specialists on the Proteaceae have suggested that the three Melanesian species were generically misplaced, and careful reexamination supports this viewpoint. It is now apparent that a distinct group within the subfamily Grevilleoideae is composed of the generaEuplassa(endemic to South America),Sleumerodendron(a monotypic New Caledonian genus),Gevuina(based on a single South American species but recently expanded to include two other species from Queensland and New Guinea), and the three questionable Melanesian species. A review of this cluster of taxa indicates thatGevuinashould again be interpreted as restricted to South America and that the generic nameBleasdaleaF. v. Muell. ex Domin should be adopted for a group of five species extending from Queensland and New Guinea to the New Hebrides and Fiji. The relationships of the four genera are discussed and withinBleasdaleafour new combinations are proposed:B. bleasdalei(F. v. Muell.),B. ferruginea(A. C. Sm.),B. vitiensis(Turrill), andB. lutea(Guillaumin).Kermadecia, very distinct from the four genera under present consideration, is again interpreted as a New Caledonian endemic.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14045.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

Pyrrhopappus carolinianusandHemihalictus lustransconstitute a mutualistic association: the early morning flowering ofPyrrhopappusprovides the matinal bee with a nearly exclusive pollen source, although other plants must be visited for nectar. FemaleHemihalictus, the primary pollen vector, tear open the anthers and remove the pollen before it is available to other bees. The foraging behavior of the bee insures cross‐pollination. The flight pattern of the bees generally restricts the pollen dispersal range. If cross‐pollination fails, then autogamy results from twisting of the styles that brings the stigmas in contact with the pollen presented on the styles of other florets.Schinia mitisis an important predator of the capitulae ofP. carolinianus.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14046.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

This study deals with the occurrence and relative abundance of four different types of abortive ovules in three species ofQuercus.It was found that, contrary to previous literature, fertilization does not always occur in the abortive ovules. The most common type of abortive ovule is the one in which a normal embryo sac develops, yet fertilization does not occur. The absence of embryo sacs and the occurrence of empty embryo sacs account for abortion in other ovules. All types of abortive ovules can occur in the same ovary. It is proposed that all of the ovules that develop a normal embryo sac are potential seeds, but the first one to be fertilized suppresses the normal development of the others.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14047.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

Ten mutant sites have been located in linkage group II ofSordaria fimicola, nine of them affecting fertility. Two different regions of the chromosome are marked with allelic mutations or mutant sites in closely linked loci involved in sexual reproduction. Mutants of one of these two regions also have an arginine deficiency. Crosses between the self‐sterile mutants of each region yield hybrid perithecia containing asci with four spores of each parental genotype and few or no asci with recombinant spores. The bearing that these findings have upon the evolution of heterothallism is discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14048.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

The Asiatic genusDecaschistiahas traditionally been placed in the tribe Hibisceae, but it is shown that this genus has a combination of characters that does not permit it to be accommodated either in the Hibisceae or in any other tribe of the Malvaceae. A new tribe, the Decaschistieae Fryx., is therefore described and distinguished from the other four tribes currently accepted in the Malvaceae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14049.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

The floral morphology and anatomy of one representative of the Parnassioideae and two of the Brexioideae are described, and some of the recent literature dealing with the Saxifragaceaesensu latois reviewed. Comparison of the floral structure inParnassiato that typical of the Saxifragoideae, the subfamily constituting the Saxifragaceaesensu strictoand which, therefore, may be considered to show the basic saxifragaceous characteristics, reveals little similarity.Parnassiadiffers in pattern of both sepal and androecial vascularization, vascularization and degree of connation of the carpels, height in the gynoecium to which ventral bundles remain compound, possession of nectariferous staminodia, and the absence of epidermal appendages.BrexiaandIxerba(both of the Brexioideae) are strikingly dissimilar in floral structure and probably should be dissociated. While the position ofIxerbais problematical, it shares more floral characters with the Escallonioideae than with eitherBrexiaor the Saxifragoideae and is better associated with that taxon. In bothParnassiaandBrexiathe vascular pattern suggests derivation of the androecium from a fascicled condition: the vascular supply of each filament consists of a cylinder of closely associated collateral bundles, and each staminodial set receives a single vascular complex which subsequently divides into as many vascular strands as there are staminodia in the set.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14050.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

Development of a typical pseudoparaphysate centrum inDidymosphaeria sadasivaniiRamachandra‐Reddy indicates that this ascomycete is properly placed in the Pleosporaceae despite the fact that forcible discharge of ascospores from bitunicate asci has not been demonstrated. The relatively thin‐walled asci releasing ascospores within the ascocarp inD. sadasivanii, as inCochliobolusspp., probably were derived by reduction from the bitunicate type. Ascocarps matured on malt agar slants but developed more rapidly and normally on autoclaved alfalfa stems inoculated in medicine bottles and transferred to moist filter paper in large petri dishes when covered by mycelium.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14051.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

The ovules inDrimys winterivar.chilensisandD. lanceolataare consistently vascularized entirely by the ventral bundles, without contribution from the dorsal bundle(s) as generally assumed. The ovules are initiated in two rows, without any in “median” position. Post‐initiatory differential growth of the carpel wall brings the lowermost ovules into apparently median position at maturity. The anomalous vascular supply to the lowermost ovules is thought to be related to concurrence of delayed initiation and development of these ovules with delayed differentiation of the vascular supply.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14052.x

出版商:Wiley    

年代:1975

数据来源: WILEY