摘要:

The floral biology of eight species ofMagnolianative to the United States is described. The flowers are protogynous. They are pollinated by several species of beetles that enter buds as well as closed and open flowers to feed on nectar, stigmas, pollen, and secretions of the petals. Individual flowers persist from two to four days and undergo a series of petal, stigma, and stamen movements that assure pollination by beetles. It is suggested that the flowers ofMagnoliaare highly specialized for exclusive pollination by beetles. These specialization mechanisms produce large quantities of food for the beetles and deny other types of insects (bees, moths, etc.) access to the flowers at critical stages in the pollination process, i.e., when stigmas are mature and pollen is shed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1974.tb12321.x

出版商:Wiley    

年代:1974

数据来源: WILEY

摘要:

In bothChamaedorea seifriziiBurret andC. cataractarumMartius each adult foliage leaf subtends one axillary bud. The proximal buds inC. seifriziiare always vegetative, producing branches (= new shoots or suckers); and the distal buds on a shoot are always reproductive, producing inflorescences. The prophyll and first few scale leaves of a vegetative branch lack buds. Transitional leaves subtend vegetative buds and adult leaves subtend reproductive buds. Both types of buds are first initiated in the axil of the second or third leaf primordia from the apex, P2 or P3. Later development of both types of bud tends to be more on the adaxial surface of the subtending leaf base than on the shoot axis. Axillary buds ofC. cataractarumare similarly initiated in the axil of P2 or P3 and also have an insertion that is more foliar than cauline. However, all buds develop as inflorescences. Vegetative branches arise irregularly by a division of the apex within an enclosing leaf (= P1). A typical inflorescence bud is initiated in the axil of the enclosing leaf when it is in the position of P2 and when each new branch has initiated its own P1. No scale leaves are produced by either branch and the morphological relationship among branches and the enclosing leaf varies. Often the branches are unequal and the enclosing leaf is fasciated. The vegetative branching inC. cataractarumis considered to be developmentally a true dichotomy and is compared with other examples of dichotomous (= terminal) branching in the Angiospermae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1974.tb12322.x

出版商:Wiley    

年代:1974

数据来源: WILEY

摘要:

The discovery of pedunculate specimens of pollen organDolerothecain close association withMyeloxylon‐type pinnae andAlethopteris‐type pinnules provides evidence for the reconstruction of a petrified medullosan frond and the attachment of the microsporangiate fructification. Specimens ofDolerotheca villosaandD. formosafrom Middle and Upper Pennsylvanian age strata of North America are borne on slender peduncles with anatomical features and vascularization identical to those of some level in aMyeloxylon‐Alethopteris‐type frond. Reconstruction of the frond reveals a large, repeatedly dichotomising organ that bears penultimate pinnae and ultimate pinnules in a pinnate arrangement. Examination of pinnules on the surface of coal ball material indicates that they conform to the compression genusAlethopteris.Identical numbers and arrangement of vascular bundles together with identical anatomical features and multicellular hairs indicate that theDolerothecacampanulum is borne in the position of a penultimate pinna. A reconstruction of the frond with a proposed polled organ attachment is included.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1974.tb12323.x

出版商:Wiley    

年代:1974

数据来源: WILEY

摘要:

Well‐preserved stages of microgametophyte development are described from pollen produced by the Paleozoic seed fern family Callistophytaceae. Microgametophyte development in both the Middle Pennsylvanian pollen organIdanothekionand Upper PennsylvanianCallandriuminvolved the initial production of an axial row of at least three small prothallial cells proximally and a large embryonal cell distally. The arrangement and form of these cells is like that present in some extant genera of the Pinaceae. The prothallial cells were relatively large in comparison with extant gymnosperms, occupying the entire region of the cap‐pus, and were apparently all primary. Evidence is presented that inCallandriumfurther development involved an anticlinal division of the large distal cell (antheridial initial) into a small generative cell contained within a larger tube cell. Previously described microgametophytes of the late Paleozoic order Cordaitales are reinterpreted and are shown to consist of an embryonal cell and three to four discoidal prothallial cells in an axial row like that of the Callistophytaceae. Microgametophytes thus far described from the Paleozoic are remarkably modern in appearance and provide no evidence to support the generally held view that the seed plant microgametophyte is an extremely reduced sexual phase that has arisen through the loss of almost all of the vegetative cells and the sterile outer cells of the antheridium. Evidence to support or refute this view will depend upon the discovery of microgametophytes from older groups of seed plants than those for which they are now known.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1974.tb12324.x

出版商:Wiley    

年代:1974

数据来源: WILEY

摘要:

Karyogamy is described inOedogonium cardiacumfrom ultrastructural studies. Close proximity of the two gamete nuclei in the fusion cell is established by plasmogamy, whereas karyogamy appears to be initiated by multiple contacts formed between the outer membranes of the adjoining nuclear envelopes. Blebs of endoplasmic reticulum (ER) originate from the outer membrane of each nuclear envelope; these ER blebs presumably contact and fuse with the outer membrane of the nuclear envelope of the opposing nucleus. This is followed by the fusion of the inner membranes of the opposing nuclear envelopes, thereby resulting in a series of small connective bridges between the two gamete nuclei. It is estimated that in this manner 30–50 bridges are formed, perhaps many more. Several of these bridges enlarge relative to the others; one presumably becomes the major connection between the fusing nuclei. As it continues to enlarge, any organelles positioned between the fusing nuclei are pushed aside. There is also evidence, particularly in later stages of karyogamy, that the smaller connective bridges fuse to form larger ones. Temporary cytoplasmic channels often result at the juncture of fusion. In other instances, isolated inclusions of cytoplasm may be delimited by remnants of nuclear envelope deep within the developing zygote nucleus; these inclusions disappear with subsequent development. Throughout karyogamy the contribution of the male gamete nucleus is readily recognized by the characteristic appearance of its highly condensed chromatin. Ultimately, however, this distinction is lost and the content of the mature zygote nucleus assumes a more uniform appearance very similar to that of an egg nucleus. The complete process of fertilization inOedogoniummay occur within 15 min of mixing the spermatozoids with eggs.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1974.tb12325.x

出版商:Wiley    

年代:1974

数据来源: WILEY

摘要:

The percentages of germination ofHeleochloa alopecuroides(Pill and Mitterp) Host seeds were tested in various controlled atmospheres of He, N2, and CO2. Atmospheres of 16.7%, 33.3 %, and 88.9 % of each of these gases (thus reducing O2concentrations to 17.5 %, 14.0 %, and 2.3% respectively) were introduced into 1000‐ml stoppered vacuum flasks, each containing 100 seeds placed on substrates of either sterilized soil or filter paper. The flasks were placed in growth chambers with an 8‐hr light period at 20 C and a 16‐hr dark period at 5 C. The germination rate was accelerated directly with increased concentrations of He and N2but was retarded by increased percentages of CO2. Control flasks eventually reached nearly the same percentages of germination as those of He and N2but at a later point in time.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1974.tb12326.x

出版商:Wiley    

年代:1974

数据来源: WILEY

摘要:

We obtained considerable evidence in earlier work that inhibition of nitrification begins during old‐field succession and increases to a maximum in the climax (Rice and Pancholy, 1972, 1973). Moreover, we found that tannins and tannin derivatives appear to be important inhibitors of nitrification. In the present project, other potential phenolic inhibitors of nitrification were identified in acetone extracts of entire plants of most herbaceous species and leaves of tree species important in an intermediate stage of succession and the climax in three vegetation types in Oklahoma. Attempts were made also to identify potential inhibitors in acetone extracts of soil from the top 15 cm of the oak‐pine climax. Seventeen potential inhibitors were identified from the eleven important species of plants surveyed. These were mostly phenolic acids and flavonoids, but one coumarin compound, scopolin, was found in high amounts in several species. The potential inhibitors were most common in green tops or green leaves, but roots, dead tops (of previous year), and dead leaves had high amounts of some compounds. Caffeic and ferulic acids were prominent in dead leaves or dead tops, and one flavonoid, myricetin, occurred in sizeable amounts in dead tops ofSorghastrum nutans.The aglycones of most of the compounds were tested against nitrification in soil suspensions, and all completely inhibited oxidation of NH+4to NO−2byNitrosomonasat concentrations as low as 10−6to 10−8M. Oxidation of NO−2to NO−3byNitrobacter, however, was affected much less severely by these inhibitors. The greater resistance ofNitrobacteris not significant biologically because inhibition of the first step carried out byNitrosomonaseffectively inhibits the entire process of nitrification. The 3‐glucoside of quercetin, isoquercitrin, inhibited the activity ofNitrosomonascompletely at the same concentration as quercetin. We found a compound in large quantities in the oak‐pine climax soil which appeared in all tests to be a flavonoid aglycone, but we were never able to identify it to our satisfaction. This substance was extremely inhibitory to germination and seedling growth of ‘Crimson Giant’ radish seeds. These have hard seed coats and germinate very rapidly so most inhibitors do not affect their germination at all. It is likely that some, if not all, of the nitrification inhibitors identified may be important in inhibition of nitrification in the later stages of succession and in the climax along with the tannins.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1974.tb12327.x

出版商:Wiley    

年代:1974

数据来源: WILEY

摘要:

Cells of the mature root exhibit arrest within the G1 and G2 periods of the mitotic cycle. The number of cells arrested with a 2C or 4C DNA amount in mature tissue was compared with that in meristems of excised primary root tips deprived of carbohydrate. Results from four plant species are described. Cells in mature tissue of seedling roots ofViciaandPisumexhibited arrest predominately at the 4C while those ofTriticumandHelianthusarrested preponderantly at the 2C DNA level. The proportion of cells arrested at the 2C and 4C levels in mature root tissue was specific for each species tested. In each species the cycle stage where most cells arrested was the same in carbohydrate‐deficient root meristems as in mature root tissue; consequently, most meristematic cells are preconditioned or predetermined to arrest in a specific mitotic period. A test system was developed inPisumin which the predominant period of arrest was altered by the removal of the cotyledons. The predominant arrest period changed from 4C to 2C in both mature root tissue and carbohydrate‐deficient root meristems with cotyledon removal and indicated that mature root cells are preconditioned while meristematic as to where they will eventually arrest in the mitotic cycle.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1974.tb12328.x

出版商:Wiley    

年代:1974

数据来源: WILEY

摘要:

Diversity of pollen apertures in 35 families of the ranalean complex is compared through a series of representative scanning electronmicrographs, and the evolution of pollen aperture types in primitive angiosperms is outlined. A classification of pollen apertures found in the ranalean complex is presented, and ten basic aperture types are recognized: anasulcate, anatrichotomosulcate, zonasulculate, anaulcerate, catasulcate‐cataulcerate, inaperturate, disulculate‐diulculate, forate, colpate, and porate. Evidence is adduced for the primitive (ancestral) status of anasulcate pollen, and transitional stages in the evolution of other pollen aperture types in the ranalean complex are examined. From an early stock of ranalean angiosperms with anasulcate pollen, there appears to have been development of a number of interesting but evolutionally dead‐end lines, represented among others by zonasulculate, anaulcerate, and catasulcate‐cataulcerate pollen types. The most important evolutionary trend in early angiosperm pollen seems to have been the development of inaperturate pollen grains in many families of primitive angiosperms, from which there was a second major radiation of aperture types, including evolution of disulculate and forate pollen. Comparative study of pollen apertures observed in living primitive angiosperms suggests a de novo origin of the uniquely angiospermous (dicotyledonous) colpate pollen type from such inaperturate pollen.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1974.tb12329.x

出版商:Wiley    

年代:1974

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1974.tb12330.x

出版商:Wiley    

年代:1974

数据来源: WILEY