摘要:

The inflorescence ofHouttuynia cordataproduces 45–70 sessile bracteate flowers in acropetal succession. The inflorescence apical meristem has a mantle‐core configuration and produces “common” or uncommitted primordia, each of which bifurcates to form a floral apex above, a bract primordium below. This pattern of organogenesis is similar to that in another saururaceous plant,Saururus cernuus. Exceptions to this unusual development, however, occur inH. cordataat the beginning of inflorescence activity when four to eight petaloid bract primordia are initiated before the initiation of floral apices in their axils. “Common” primordia also are lacking toward the cessation of inflorescence apical activity inH. cordatawhen primordia become bracts which may precede the initiation of an axillary floral apex. Many of these last‐formed bracts are sterile. The inflorescence terminates with maturation of the meristem as an apical residuum. No terminal flowers or terminal gynoecia were found, although subterminal gynoecia or flowers in subterminal position may overtop the actual apex and obscure it. Individual flowers have a tricarpellate syncarpous gynoecium and three stamens adnate to the carpels; petals and sepals are lacking. The order of succession of organs is: two lateral stamens, median stamen, two lateral carpels, median carpel. The three carpel primordia almost immediately are elevated as part of a gynoecial ring by zonal growth of the receptacle below the attachment of the carpels. The same growth elevates the stamen bases so that they appear adnate to the carpels. The trimerous condition inHouttuyniais the result of paired or solitary initiations rather than trimerous whorls. Symmetry is bilateral and zygomorphic rather than radial. No evidence of spiral arrangement in the flower was found.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06385.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

The fine structure of the pollen grain ofTillandsia caput‐medusaeMorr. (Bromeliaceae) prior to germination has been studied. The development, after the first mitosis, is here schematized in three stages which are in accordance with the main steps described in angiosperms. The ultrastructural modifications occurring in the generative and vegetative cells are discussed in view of their different destiny. The results obtained are compared with the data known about tropical orchids and epiphyteic plants likeTillandsia. The following differences have been observed: a large vacuole in the vegetative cell; rapid thinning of the wall between the generative and vegetative cells; great quantity of ribosomes and rough endoplasmic reticulum surrounding the vacuoles in the generative cell. The above‐listed ultrastructural features may have a meaning, considering the peculiar environmental conditions in which the epiphytism ofTillandsiais achieved.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06386.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Seedlings ofAtriplex hortensiswere studied to ascertain; 1) in which organ the primary thickening meristem (PTM) first differentiates; 2) the direction of differentiation of the PTM, and 3) the pattern of differentiation of conjunctive tissue. The PTM initially differentiates in pericycle of the primary root base 11 days after emergence of the primary root. It then differentiates in the transition region of the hypocotyl, mostly in cells of pericycle between pairs of vascular bundles. In the upper hypocotyl, PTM differentiates by day 20 in the inner layer of cortical parenchyma. In the epicotyl, PTM apparently differentiates in the inner layer of cortex, by day 24. Desmogic xylem differentiates from radial files of internal conjunctive tissue cells and desmogic phloem differentiates opposite desmogic xylem strands from newly formed cells of external conjunctive tissue. No interfascicular cambium differentiates in the root, hypocotyl, or epicotyl.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06387.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

The mosquito fern,Azolla filiculoidesLam., was grown in a growth chamber on a nitrogen‐free culture solution at 24 C under the following photoperiod: 16 hr light/8 hr darkness. Shoot tips were fixed every 2 hr for 24 hr to determine the mitotic index for the apical cell, immediate derivatives, and remaining cells to the level of the first leaf or lateral shoot primordium. Mitotic indices were 6.9%, 6.5% and 6.3%, respectively. The colchicine method was employed to determine the cell‐cycle durations and duration of mitosis for the same populations of cells. The cell‐cycle duration and duration of mitosis of the apical cell were 28.2 hr and 2.8 hr, respectively; for the immediate derivatives, 26.7 hr and 2.5 hr; for the remaining cells, 23.6 hr and 2.1 hr. Conclusions: the apical cell is as mitotically active as its immediate derivatives, and there is no evidence of a quiescent apical cell.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06388.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

The chalazal area is confirmed as the site of initial water entry into prickly sida (Sida spinosaL.) seeds. Very early during imbibition of water, a kidney‐shaped area of the seed coat separates from underlying cells forming a blister. This blister may also be induced in dry seeds (both afterripened and nonafterripened) when pressure is applied to the chalazal area. Blisters form more readily on afterripened seeds than on nonafterripened seeds, however, and the event is correlated with an increase in seed coat permeability to water. Immediately beneath the palisade layer of the blister lies a single layer of subpalisade cells. This layer is observed only in the region of blister formation. As the blister separates, the end walls of the subpalisade cells remain attached to the floor of the palisade layer. The subpalisade cells are thereby broken open, and their contents disgorged into the blister lumen. Evidence indicates that this separation of the palisade and subpalisade layers in the chalazal area initiates imbibition of water by prickly sida seeds.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06389.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Saxicolous cryptogam communities were sampled quantitatively on two Potomac River island habitats in June of 1980. As a result of air pollution stress, the community on one island was found to be much simpler than that found on the other island. Two relatively pollution‐tolerant foliose lichen species,Xanthoparmelia conspersaandPseudoparmelia baltimorensis, were found to dominate the communities on both islands. An examination of niche breadth and position along a light intensity gradient demonstrated thatP. baltimorensiswas most frequent at low light intensities andX. conspersawas most frequent at high light intensities. However,X. conspersaexhibited a niche shift toward intermediate light intensities in the species‐poor community, likely the result of reduced competitor diversity in this community since the intermediate light intensities supported the greatest number of species in the species‐rich community. Niche overlap between the two species was found to occur at lower light intensities in the species‐poor community, suggesting thatX. conspersais more likely to appropriate intermediate light intensities in this community. The significance of competition as a regulatory factor in lichen communities has not been fully appreciated. Since lichens and other cryptogams are frequently used as indicators of environmental quality, competitive processes in naturally occurring lichen communities must be thoroughly understood before changes in species distribution that apparently result from disturbance can be properly interpreted.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06390.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

The subcellular organization of zoospores released from sessile, parasitic sporangia ofCaulochytrium protostelioideswas studied with light and electron microscopy. A single flagellum is posteriorly directed but laterally inserted into the cylindrical motile zoospore. A striated rhizoplast attaches the proximal end of the kinetosome to a specialized region of the nuclear envelope. A system of rough endoplasmic reticulum, smooth endoplasmic reticulum, dictyosomes and bristle‐coated vesicles are associated with the one to several pulsating vacuoles typically located near the flagellar apparatus. The microbody‐lipid globule complex (MLC) comprises one to many lipid globules. An extensive microbody branches around each lipid globule and encloses a portion of the rhizoplast. A reticulum of smooth surfaced cisternae interdigitates among the branches of the complex microbody, and cisternae are opposed to the surface of lipid globules opposite the microbodies. Mitochondria with predominantly circular profiles are scattered throughout the zoospore body, but several are always adjacent to the microbody, and hence, are also part of the MLC. Ribosomes are uniformly distributed throughout the zoospore, and one to several cisternae of rough endoplasmic reticulum are adjacent to the nuclear envelope. Zoospores ofC. protostelioidesare similar to several other chytrid zoospores, which also have the same type of microbody‐lipid globule complex, but yet are structurally distinct from any other chytrid zoospore.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06391.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Nexine and intine development inSilene alba(Caryophyllaceae) was investigated by electron microscopy and enzyme cytochemistry. Nexine‐2 forms by deposition of sporopollenin along unit membrane lamellae closely associated with the microspore plasma membrane in the late tetrad stage. After the callose wall dissolves, electron density increases along the tangentially oriented fibers of the proximal primexine, forming nexine‐1. When the exine is essentially complete, the intine begins to develop. In the nearly mature microspore, acid phosphatase activity appears in the peripheral cytoplasm just prior to its extrusion into the intine of the mature pollen grain.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06392.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Early stages of pseudothecium development consist of small pseudoparenchymatous stromata in which ascogonia differentiate. Deeply staining cells in the apical region of the young pseudothecium elongate to form pseudoparaphyses, which grow down to fill the centrum. Ascogenous hyphae grow out from ascogenous cells, located in the basal plectenchyma, and croziers arise and proliferate from the ascogenous hyphae. Bitunicate asci grow up among the pseudoparaphyses and forcibly discharge two‐celled hyaline ascospores at maturity. Because centrum development inDidymella bryoniae(Auersw.) Rehm is pseudoparaphysate, the causal agent of gummy stem blight in watermelon is properly placed in the order Pleosporales. The placement of this species inDidymellaon the basis of theAscochyta cucumisFautr. et Roum. anamorph is supported by centrum structure.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06393.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Ptyxis, phenology, and leaf trichomes are described for 43 species representing all ten genera in the Cycadales. The typical annual growth sequence is: leaf flush production, cataphyll production, reproductive production, and finally cataphyll production in all taxa exceptStangeriawhich does not have cataphylls and produces leaves one at a time throughout the year. The leaf and cataphyll bases are slightly winged except inZamiaandCeratozamia, which have well developed stipules, and inStangeria, which has a distinctive adaxial, stipular hood on the leaf bases. Longitudinal ptyxis of the whole leaf is of four types: circinate (only inBowenia); erect (Cycas, Dioon, Encephalartos, Lepidozamia, Macrozamia, Microcycas, and someZamiaspp.); inflexed (Stangeria, Ceratozamia, and someZamiaspp.); and reflexed (rarely found inCycasandDioon). The pinnae are oriented so that the horizontal ptyxis is conduplicate in all taxa exceptBoweniaandCycaswhere it is involute. The individual pinnae are circinate inBoweniaandCycas, conduplicate inStangeria, and flat in all other taxa. The pinnules ofBoweniaare also flat. Leaf trichomes are of six types: transparent unbranched; transparent branched; colored unbranched; colored branched; colored idioblastic; and short colored curved.Cycashas only transparent branched (unequally) and unbranched.Ceratozamia, Dioon, Encephalartos, andStangeriahave transparent and colored trichomes, both unbranched.Bowenia, LepidozamiaandMacrozamiahave short colored curved hairs and transparent unbranched hairs.Macrozamiais the only taxon with colored idioblastic trichomes.ZamiaandMicrocycashave transparent and colored hairs. Both trichome types occur branched and unbranched. Because of its decompound leaf, circinate ptyxis, cones on short determinate branches and other distinct characters the family Boweniaceae D. Stevenson fam. nov. is described. This family contains one genus:Bowenia.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06394.x

出版商:Wiley    

年代:1981

数据来源: WILEY