摘要:

A periodic acid‐Schiff's substance present in the micropylar end of the ovules ofPaspalum orbiculareandP. longifoliumwas further studied by light and electron microscopy of glutaraldehyde‐osmium‐fixed and freeze‐substituted, osmium‐fixed tissues. The PAS substance is water soluble and is found in intercellular spaces between the nucellus and inner integument, the inner and outer integuments, the outer integument and ovary wall, and in the micropyle. Structurally the substance consists of fibrils embedded in a dense, amorphous matrix and may be associated with membranous structures in special layers between the plasmalemma and the cell wall in nucellar and integumentary cells. Part of the water soluble substance is believed to be secreted from the nucellar and integumentary cells. A large amount of this substance may be formed as a result of the dissolution of about one third of the distal micopylar portion of the outer integument prior to anthesis. Many of the electron‐dense fibrils seem to be fibrillar intercellular substances and others appear to originate from the cell walls, including the cuticle. Both the matrix and the fibrils may be chemically heterogeneous and together form a mucilagenous substance which may facilitate the final growth of pollen tubes in these two species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb11937.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

H. angulatais a scale‐covered, asymmetrical green unicell with two laterally attached, anisokont flagella. In recent years it has been classified in the Prasinophyceae. The flagellar apparatus replicates, and the cell begins to cleave at the side opposite the flagella before the nucleus can be perceived to be in prophase. The flagellar apparatuses separate, and the extra‐nuclear development of the spindle occurs from the regions occupied by rhizoplasts. Rhizoplasts or partial rhizoplasts lie at the flat metaphase spindle poles. By metaphase, the cell has already elongated to the extent that it is nearly twice as long as at interphase. The spindle and the cell itself elongate greatly during anaphase with a concomitant further separation of the flagellar pairs. Although the interzonal spindle persists during cytokinesis as in charophycean algae,H. angulatais similar in flagellar scale morphology and other characteristics to the chlorophyceanPlatymonas, which has a collapsing interzonal spindle at telophase, a phycoplast, and a wall‐like theca, which develops by the fusion of small stellate scales. It is hypothesized that the collapsing telophase spindle and phycoplast evolved in green flagellates similar toPlatymonas, in which cell and spindle elongation became restricted by a cell wall that evolved from stellate scales similar to those inHeteromastix.Such walled flagellates are then visualized as having eventually given rise toChlamydomonasand to the entire range of chlorophycean algae with phycoplasts. It is pointed out that the hypothesis has a number of implications by which its validity could be judged when sufficient information becomes available.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb11938.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

The primary vascular connection between primary and secondary root ofGlycine max(L.) Merr. was derived from stelar parenchyma and pericycle. Inner stelar parenchyma, associated with the parent metaxylem and outer stelar parenchyma adjacent to the pericycle, were resonsible for the histogenesis of the primary xylem connection. Acropetal maturation of the diarch xylem connection occurred after the lateral root emerged from the parent root. Development of tetrarchy occurred distal to the diarch xylem connection. The concentric primary phloem connection was derived from the pericycle and outer stelar parenchyma. Acropetal maturation of the primary phloem connection occurred prior to lateral root emergence from the parent root. Secondary growth quickly augmented the primary vascular connection. A substantial amount of mature secondary xylem formed prior to maturation of the secondary phloem. The structure of the primary and secondary vascular connections is described.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb11939.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Nematodes in the bases of lateral root primordia ofGlycine max(L.) Merr. caused abnormal vascular connection development. All lateral roots with single infections at their points of origin in the primary root—the sample included 28 specimens from 2.0–25.0 cm in length—were triarch. The control lateral root sample contained one triarch and 36 tetrarch roots. Affected lateral roots had a peculiar orientation of the xylem poles. Up to 600–700μm from the infection site the three xylem poles were oriented at 90°, 90°, and 180° angles. Distally the angle between xylem poles shifted to 120°. All control and infected primary roots were tetrarch. Statistical comparison of three parameters, root diameter, vascular cylinder diameter, and primary xylem cross‐sectional area showed that only xylem cross‐sectional area was significantly different between normal tetrarch and affected triarch lateral roots.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb11940.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

The results of a light and electron microscopic study of the caryopsis coat and aleurone cells in ungerminated, unimbibed rice (Oryza sativa) caryopses are presented. Surrounding the rice grain is the caryopsis coat composed of the pericarp, seed coat and nucellar layers. The outermost layer, the pericarp, consists of crushed cells and is about 10μm thick. The seed coat, interior to the pericarp, is one cell thick and has a thick cuticle. Between the seed coat cuticle and endosperm are the remains of the nucellus. The nucellus is about 2.5μm thick and has a thick cuticle adjacent to the seed coat cuticle. Interior to the caryopsis coat is the aleurone layer of the endosperm. The aleurone completely surrounds the rice grain and is composed of two cell types—aleurone cells that surround the starchy endosperm and modified aleurone cells that surround the germ. The aleurone cells of the starchy endosperm contain many aleurone grains and lipid bodies around a centrally located nucleus. The modified aleurone cells lack aleurone grains, have fewer lipid bodies than the other aleurone cells, and contain filament bundles (fibrils). Plastids of aleurone cells exhibit a unique morphology in which the outer membranes invaginate to form tubules and vesicles within the plastid. Transfer aleurone cells are not observed in the mature rice caryopsis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb11941.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

The designationStigmaria ficoidesis restricted to casts and impressions. Petrifactions ofStigmaria arnoldiisp. n. occur in Pennsylvanian age strata in Trout Creek Pass, Colorado. The rootlet gaps of this species appear narrow and elongate in both cross and longitudinal sections. Rootlet traces are contiguous with the secondary xylem to its outer margin and are surrounded by a small parenchyma sheath in the middle cortex. The outer cortex consists of an inner layer of primary tissue and a relatively thick zone of periderm.S. arnoldiimost closely resembles material described asS. ficoidesfrom England. Various stigmarian characters are evaluated with regard to their systematic or ontogenetic significance.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb11942.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Photoperiodic floral induction inXanthium, achieved by subjecting the plants to two long nights, is accompanied by a transient change of the phyllotaxis from the (2, 3) contact parastichy pattern of vegetative plants, to a (3, 5) pattern during the transition. To specify the phyllotaxis, two parameters were estimated from transverse sections of apical buds of control and treated plants: the divergence angle,α, and the plastochron ratio,a.The plastochron ratio decreased progressively during transition from the vegetative to the reproductive state of growth, froma= 1.48 initially toa= 1.15 six days after the beginning of induction. The divergence angle was not altered during the transition. This change in phyllotaxis is interpreted as a change in the relative positioning of leaf primordia on the transitional apex. This transient change appears to be identical with the previously described long‐term change of the phyllotaxis ofXanthiumbrought about by treatment of plants with gibberellic acid.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb11943.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

A further study ofPhysoderma hydrocotylidisfrom California on its hostHydrocotyle ranunculoidesgives further details on its structure and development. EM micrographs reveal that the notably thin wall of the resting spore consists of an outer, an intermediate, and an inner layer. The complete wall thickness from measurements of these EM preparations is only 0.5μm, the thinnest of any knownPhysodermaresting spore. Such resting spores germinate readily in 2–5 h by the dehiscence of a broad cap and formation of a protruding endosporganium. Zoospores from the latter infect epidermal host cells and produce either the endobiotic, polycentric rhizoidal system with tenuous filaments, turbinate cells and eventually resting spores, or a hitherto unknown epibiotic, monocentric, rhizidiaceous sporangial stage. Zoospores from the latter may all bear colorless lipid globules or all faintly orange‐colored ones.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb11944.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

The pteridosperm (Medullosaceae) pollen organSullitheca dactyliferagen. et sp. n. is described from middle Pennsylvanian coal balls. The proximally fused units of the obpyriform compound synangium separate and extend distally as finger‐like projections. Each projection contains 4–6 vertically oriented cylindrical sporangia arranged in pairs along the radius of the unit; each unit extends from the outer cover wall toward the center. The distal portion of the compound synangium is hollow as a result of the lateral separation of the centripetally and distally directed synangial units. About 40 tubular sporangia are present in all and dehiscence occurs along a lateral slit in each sporangium. Vascular strands are disposed around the periphery of the organ in addition to a single strand paralleling each sporangium. Two‐ or three‐cell trichomes and stomata are present on the organ surface. Pollen of theMonoletestype is present. A paired row of sporangia inSullithecacomposing a synangial unit is considered the homologue of a paired row of sporangia in the more compact and highly evolved genus,Dolerotheca.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb11945.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Transplants ofFragaria virginianaDuchesne, the wild strawberry, from field and woods sites, were studied under controlled laboratory conditions to determine their seed and vegetative reproduction responses under different density conditions. The following results were obtained: (1) Increased competition among high density grown plants resulted in lower total biomass when compared to low density grown plants; (2) Increased shading in high density plots resulted in a greater percentage of biomass in leaves; (3) The percentage of total biomass in reproductive organs (seed and vegetative) was higher in low density grown plants; (4) Vegetative “reproductive effort” was higher in low density plots than in high density plots while seed “reproductive effort” remained constant between the two density treatments; (5) No significant difference between plants from habitats of different successional maturity was observed under the experimental treatments. These results are discussed in relation to reproductive density response models.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb11946.x

出版商:Wiley    

年代:1977

数据来源: WILEY