摘要:

In the mitotically active vascular cambium of conifers and broadleaved trees there is tension across the radial middle lamellae. This tension seems to be important for intrusive growth of fusiform cells. In the vascular cambium ofFraxinusandRobiniathere is tension across the tangential middle lamellae also, which makes possible the increase in diameter of differentiating vessel members.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1980.tb07617.x

出版商:Wiley    

年代:1980

数据来源: WILEY

摘要:

Nyssa sylvaticaseedlings grown for a year under flooded conditions established endomycorrhizal associations withGlomus mosseae. Lowland ecotypes with endomycorrhizae showed a significant increase in biomass over non‐mycorrhizal controls; the greatest difference was in aboveground biomass. Upland ecotypes survived flooding poorly and established fewer endomycorrhizae than lowland ecotypes and did not show any enhanced growth over controls. In general, most endomycorrhizae were formed near main roots and significantly decreased in abundance with distance from the main axes of the root system. It is suggested that under flooded conditions internal oxygen transport may be limiting to mycorrhizae in the more distal roots.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1980.tb07618.x

出版商:Wiley    

年代:1980

数据来源: WILEY

摘要:

Transmission electron microscopic examination ofCephaleuros virescensKunze growing on leaves ofCamelliasp. indicates that gametes are similar to those ofTrentepohlia aurea. The gametes bear two, smooth isokont “keeled” flagella containing typical “9 + 2” axonemes and lacking scales. Flagellar insertion is apical and the parallel basal bodies overlap laterally. Each basal body is associated with a separate multilayered structure and component microtubular spline. The latter extends posteriorly beneath the plasmalemma. A nucleus, mitochondria, chloroplasts, and cytoplasmic haematochrome droplets are present. Pyrenoids and eyespots are absent. The subcellular components ofC. virescensgametes are comparable to those found in gametes ofT. aurea; however, the arrangement of basal bodies and multilayered structures differs slightly from that inT. aurea. Comparison of the fine structure of gametes fromCephaleuros, Phycopeltis, andTrentepohliaclearly indicates that the (1) mode of flagellar insertion, (2) morphology, number, and arrangement of multilayered structures, and (3) keeled flagella are common to these three genera and, thus far, unique among the green algae. Although flagellar insertion is apical, it is not bilaterally symmetrical (sensu stricto), nor is it asymmetrical (cf.CharaandNitellasperms). The arrangement may be termed “reversed bilateral symmetry” and standardization of the terminology is recommended.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1980.tb07619.x

出版商:Wiley    

年代:1980

数据来源: WILEY

摘要:

Aerenchyma development in waterloggedHelianthus annuus, Lycopersicon esculentum, andSalix fragiliswas studied. More than half of the root cortical tissue sometimes became an air cavity in willow roots which developed in water. There was no cortical aerenchyma in the terminal portion, but more advanced aerenchyma developed towards the base of the sunflower roots formed in water. Waterlogged sunflower and tomato plants developed lysigenous aerenchyma in the cortex of waterlogged stems within two days.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1980.tb07620.x

出版商:Wiley    

年代:1980

数据来源: WILEY

摘要:

The ontogeny of the major venation in the lamina ofPopulus deltoidesBartr. leaves was investigated in relation to the development of original procambial bundles, subsidiary bundles, and their derivatives. Serial sections and clearings were used to show that the midrib region is a composite structure consisting of several independent vascular bundles, each of which eventually diverges into the lamina to become a secondary vein. The sequence of events in the ontogeny of major secondary veins is: (1) an original procambial strand develops acropetally and becomes the precursor of the first vascular bundle of the midrib region of the lamina, (2) ground tissue at the forefront of acropetally developing subsidiary procambial bundles differentiates in a wavelike continuum; meristematic regions precede the acropetally developing procambial bundles, (3) discrete subsidiary bundles differentiate in the meristematic regions as they advance acropetally, (4) subsidiary bundles diverge obliquely in the lamina margin giving rise to the secondary veins in a basipetal fashion, and (5) subsequent differentiation and maturation of the secondary veins occurs within the lamina. The original procambial bundles and first‐formed subsidiary bundles become the secondary veins of the uppermost portions of the lamina, the next‐formed subsidiary bundles become the secondary veins of the middle portions of the lamina, and the last‐formed subsidiary bundles become the secondary veins of the lowermost portion of the lamina.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1980.tb07621.x

出版商:Wiley    

年代:1980

数据来源: WILEY

摘要:

Pollen of all large‐flowered neotropical loranthaceous genera and related Australian taxa (Nuytsia, Atkinsonia) were examined in the light, scanning, and transmission electron microscopes. Trilobate, deeply concave, peroblate or oblate pollen shapes are basic within the complex; triangular, slight convex, suboblate shapes are more derived features. The non‐fixiform pollen ofAtkinsoniais unique within the family. Most of the large‐flowered genera possess exclusively syncolpate aperture types. However, amongPsittacanthusspecies tricolpate, diplosynrugate and diplorugate apertures are also present, representing derived types for the complex. The inaperturate pollen ofAtkinsoniaappears to have developed independently within the family. Pollen sculpturing is typically non‐uniform, i.e., there are pronounced sculpturing differences in polar and equatorial regions. Uniformly sculptured pollen is restricted toAtkinsonia, Ligariaand some species ofPsittacanthus. Ultrastructurally, most exine modifications have occurred in the equatoral ektexine. Here the basic organization ranges from essentially columellaless to columellate, the latter the more derived condition. Endexine is typically thick and stratified in polar areas, thin and lamellate in peripheral and apertural regions. Similar pollen morphologies ofNuytsiaandGaiadendronsupport the idea of a transoceanic evolutionary connection between the Old and New Worlds. Pollen characters showGaiadendronto be the most primitive andPsittacanthusthe most advanced among the large‐flowered neotropical genera.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1980.tb07622.x

出版商:Wiley    

年代:1980

数据来源: WILEY

摘要:

Adenostoma fasciculatumH.&A. andCeanothus leucodermisGreen in chaparral stands of the foothill zone of Sequoia National Park, California, show a rapid decline in foliage concentrations of nitrogen over the first six years following fire. This is followed by a more gradual decline over succeeding years. Phosphorus concentrations show a similar early decline, followed by an increase in older age stands. Considerable data suggest luxury consumption of nutrients in both species following fire. Following a sharp increase in aboveground nutrients per unit ofAdenostomacanopy area for the first 16 years of growth, a plateau is reached. The contemporaneous occurrence of restricted net nutrient uptake and observed stand senescence suggest a possibility of a causal relationship. Natural chaparral fire frequencies promote fire‐cycling of nutrients at intervals consistent with periods when nutrient availability becomes limiting. The fire‐nutrient interactions are of critical importance in influencing quality and quantity of suitable browse for vertebrate herbivores.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1980.tb07623.x

出版商:Wiley    

年代:1980

数据来源: WILEY

摘要:

A new sterculiaceous wood,Chattawaya paliformisgen. et sp. n., was collected from a Middle Eocene locality in the type area of the Clamo Formation of north central Oregon. The wood differs from all known extant woods in having very large and irregularly shaped tile cells. However, other features of the xylem indicate a close natural relationship betweenChattawayaand the extant paleotropical genus,Pterospermum. It is suggested that the xylem organization of the Eocene fossil represents a more primitive condition than that observed inPterospermum. Comparative xylotomy indicates three evolutionary trends within the complex to whichChattawayaandPterospermumbelong: development of storied structure, increased uniformity in shape and size of tile cells and loss of multiseriate rays.Chattawayais part of a growing body of paleobotanical evidence indicating that the Sterculiaceae was well differentiated by the early Tertiary, but that the lineages leading to extant genera have undergone an appreciable amount of evolutionary change since the Eocene.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1980.tb07624.x

出版商:Wiley    

年代:1980

数据来源: WILEY

摘要:

The pollen morphology of 117 species and varieties ofMimuluswas examined by light and scanning electron microscopy. Five major and 8 more tentative, minor types were found based on the differential correlation of aperture type, exine morphology, pollen grain diameter and other characters: type 1—synaperturate, usually ±spiraperturate, exine perforate to microreticulate with supratectal processes; type II—trocolporate, exine microreticulate (IIa and IIb, supratectal processes absent; IIa, mean polar axis 16–19 μm; IIb, mean polar axis 25–35 μrn; IIc, supratectal processes present); type III—tricolpate, colpus membrane ±psilate. exine with supratectal processes (IIIa, exine microreticulate and 1.4–2.0 μm thick, polar axis ≥ 30 μm; 111b, exine densely perforate and 2.2–2.8 μm thick, polar axis ≤ 23 μm); type IV—tricolpate, colpus covered with spinulose granules (operculate), exine microreticulate with supratectal processes; type V—5–7 stephanocolpate (Va and Vb, colpus margins ±straight and nongranular; Va, exine microreticulate with supratectal spinules; Vb, exine perforate with supratectal spinules or spinulose verrucae; Vc, colpus margins ragged and granular, exine microreticulate with supratectal processes). The pollen data correlate well with geographical and macromorphological data and, where the latter are ambiguous, often provide important clues toward the resolution of conflicting interpretations of infrageneric classification and generic delimitation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1980.tb07625.x

出版商:Wiley    

年代:1980

数据来源: WILEY

摘要:

Previous studies have shown that low fluences of light accelerate starch accumulation and enhance germination ofOnocleaspores. Fluence response curves for induction of starch accumulation were compared with fluence response curves for enhancement of germination in order to determine if the two photoresponses inOnocleaspores have a common photoreceptor. Fluence response curves indicate that both responses were proportional to the log of the fluence and that the relative fluence efficiencies of the four wavelength regions tested were similar for induction of both germination and starch accumulation. Red (600–720 nm) irradiation was the most efficient, while green (500–600 nm), blue (400–520 nm), and far‐red (720–900 nm) irradiations showed a decreasing order of efficiency for induction of the responses. A correlation coefficient between the amount of starch accumulated as a result of red irradiation and the final percent germination was calculated to be 0.964. These results support the hypothesis that a common photoreceptor mediates both photoinduced germination and starch accumulation. 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) inhibits photosynthesis by blocking the flow of electrons from Photosystem II to Photosystem I. At 0.1 mM DCMU failed to inhibit both photoinduced starch acumulation and germination. This result and the greater efficiency of red than blue light, the low fluence functional for induction, and the fluence dependency argue against the participation of photosynthesis in photoinduced starch accumulation. A similar conclusion has been previously drawn for photoenhancement ofOnocleaspore germination. Additionally, the effects 0.01–1.0 mmcycloheximide and 100 μl/l ethylene on photoinduced starch accumulation were investigated. Neither agent inhibited starch accumulation, whereas both substances inhibited germination 70–90% when applied at a time coincidental with the period of rapid starch accumulation. These results indicate that the photoinduction of starch accumulation does not have an ethylene sensitive stage nor does it require protein synthesis as does photoenhancement of germination ofOnocleaspores.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1980.tb07626.x

出版商:Wiley    

年代:1980

数据来源: WILEY