摘要:

Macrozamia communisis a common cycad that occurs in eastern New South Wales, Australia, where it forms an understory in various forest or woodland communities. Leaf number of reproductive individuals as well as of nonreproductive ones, taken as an indication of size class, varies clinally from north to south, with reproductive individuals in southern populations having mean leaf numbers about 12 times greater than those at the northern end of the range of this species. Female cone size and mature ovule weight appear to vary also along this gradient. Using leaf number as a predictor of sexual maturity, from 37 to 100% of the individuals present in a population were judged to be mature. The percent of mature individuals participating in the 1987 coning episode ranged from none in three southern populations to 68% elsewhere. In 9 of 10 samples more males than females participated in the 1987 coning episode, with a collective sex ratio slightly male biased for all populations sampled. In three population samples average cone numbers for male and female plants were equal. In two samples males produced more cones per plant than females. Leaf numbers of males and females in individual populations were equal. Few individuals producing cones in 1987 showed evidence of recent prior cone production, suggesting that successive cone production by both sexes is separated by an interval of several years. The periodicity with which fire is used as a fire suppression method may affect the frequency of cone production in some populations, perhaps preventing it entirely. The apparent absence of recruitment in some populations may result from long‐term seed collection by humans for horticultural purposes as well as the very poor seed dispersal that appears to characterize this cycad throughout its range. The weevilTranes internatuswas observed occupying the internal tissues of female cones; this insect may be involved in the pollination ofM. communis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13531.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Iris fulvaKer. Gawler andIris hexagonaWalter have overlapping geographic ranges in Louisiana. In areas of overlap hybrids are fairly common.Iris hexagonaoccupies the borders of freshwater marshes of southern Louisiana whileI. fulvacan be found farther north along edges of natural levees, canals and swamps. Where the natural levee penetrates the marsh, natural hybridization can occur betweenI. hexagonaandI. fulva.It has been suggested that one principal explanation for the segregation of the two species is thatI. fulvagrows best in semishade andI. hexagonagrows best in full sun. A greenhouse study was conducted using rhizomes collected from the field to test this hypothesis and determine the relative shade tolerance of two natural hybrid types.Iris fulva, I. hexagona, and the two hybrid taxa were grown under 0% (control), 50% (medium shade), and 80% (high shade) reduction of sunlight for 6 months and then harvested.Iris fulvawas found to be more tolerant of shading thanI. hexagonaand the two hybrids. Further,I. fulvawas found to grow as well in control as in medium shade. Both hybrid taxa were more shade tolerant thanI. hexagona. Iris hexagonawas greatly affected by all levels of shade. In general, the results suggest that these hybrids are intermediate to the parental taxa in terms of shade tolerance.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13532.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Deciduous and evergreen species are segregated on northeast and southwest slopes of the southern Appalachian Mountains. The segregated distributions of three ericaceous shrubs (Rhododendron maximumvalley positions;Rhododendron periclymenoideson northeast slopes;Kalmia latifoliaon southwest slopes) were compared to the respective irradiance environments. Growth patterns of field plants, and photosynthetic acclimation of each species to three irradiance treatments in a phytotron were studied.Rhododendron maximum, an evergreen species, was found to be most sensitive to high radiation. In phytotron experiments, quantum yield, light saturated photosynthetic capacity, photosynthesis per chlorophyll, and water use efficiency decreased at high ambient irradiance forR. maximum.These characteristics limit the growth ofR. maximumon high irradiance southwestern slopes. BothK. latifoliaandR. periclymenoideswere able to improve their photosynthetic performance at high ambient irradiance.Rhododendron periclymenoides, a deciduous species, was found to continue increasing leaf conductance at high irradiance without an increase in photosynthesis indicating a possible limitation by water in high light environments such as southwest slopes.Kalmia latifolia, an evergreen species, had reduced photosynthetic capacity and reduced water use efficiency when grown in low irradiance conditions which coincides with the higherK. latifoliaabundance on high light, southwestern slopes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13533.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Using pairs of pollen donors, I analyzed the growth of pollen tubes growing in different channels of the same style inErythronium grandiflorum.After 24 hr the length of pollen tubes of randomly selected pollen donors was affected by the presence of other donors. The mean pollen tube lengths of donors did not differ when taken across all of the donor pairings, but in individual pairs, pollen from one donor was often significantly longer than pollen from the other donor when tested across several recipients. Pollen tube lengths were also consistently longer for pollen paired with pollen from the same donor than when paired with pollen from other donors, apparently because of mutual stimulation between the pollen populations from the same plant. In a second experiment, the amount of pollen tube attrition after five days of growth of pollen from a donor growing near (within 3 m) the recipient depended upon the source of other pollen growing in the same style. Local pollen experienced more attrition paired with self pollen than when paired with outcross pollen. Pollen from different outcross distances also modified the attrition of local pollen, but local pollen usually outcompeted pollen from greater distances. Since the growth of local pollen was modified depending upon the source of other pollen growing in the same style, it is probable that recipient styles are selectively inhibiting pollen tubes to produce the patterns of pollen tube interaction observed. The results from these two experiments indicate that the amount of attrition for pollen can be dependent on the composition of the pollen pool. Both direct pollen tube interactions and mediation by the stylar tissue appear to affect the growth rate and attrition of pollen inErythronium.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13534.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The embryology ofHerminium monorchis(Orchidaceae) was studied using confocal scanning laser microscopy (CSLM), a new technique for embryological studies. This technique may contribute new information to plant embryology.Herminium monorchishas a monosporic embryo sac development. The mature embryo sac is 8‐nucleate. Two integuments, both 2‐layered, are formed, but only the inner takes part in formation of the micropyle. Double fertilization takes place. The primary endosperm nucleus does not divide, but remains alive at least at the 3‐celled stage of embryo development. The three antipodals do not show any sign of degeneration at this stage.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13535.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

InBrassica oleracea, sporophytic self‐incompatibility prevents germination of self pollen, or normal growth of self pollen tubes. After self‐pollination, the papillae of stigmas synthesize callose. The role of Ca++in the formation of stigmatic callose was tested by adding compounds that interact with Ca++to suspensions of pollen that were known to induce callose formation in self stigmas. The calcium channel antagonist, lanthanum, and the calcium chelating agent, EGTA, reduced or abolished the callose response to self‐pollen suspensions. In the presence of Ca++, the calcium ionophore, A23187, induced callose in stigmatic papillae when added to pollen suspensions, or alone. Therefore, callose deposition in response to incompatible pollinations appears to be a calcium‐dependent process. Pretreatment of pistils with 100μm 2‐deoxy‐D‐glucose abolished the callose response to self‐pollination, while self pollen remained inhibited and cross pollen grew normally in treated pistils. Thus, callose formation in the stigma is not an essential part of the self‐incompatibility mechanism preventing the growth of self pollen inBrassica.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13536.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Mature leaves ofArgyroxiphium grayanumexhibit an unusual structure‐function relationship. The leaves are traversed by several large channels filled with extracellular polysaccharide. Infrared spectral data suggest that the polysaccharide is mainly pectin, which is consistent with previous data based on its histochemical staining properties. The polysaccharide exhibits a very high water‐holding capacity, which appears to result in a very high leaf capacitance at high water contents and water potentials. The volume‐normalized leaf capacitance ofA. grayanumis 0.67 MPa–1over the water potential range of –0.1 to –0.5 MPa. Coupled with the low time constant for water flux within the leaves (57 sec), the high leaf capacitance ofA. grayanummay enable it to avoid rapid declines in leaf water potential. Thus, in its native bog habitat in Hawaii, the high leaf capacitance ofA. grayanummay be of benefit in terms of minimizing the development of short‐term leaf water deficits.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13537.x

出版商:Wiley    

年代:1990

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13538.x

出版商:Wiley    

年代:1990

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13519.x

出版商:Wiley    

年代:1990

数据来源: WILEY