Endogenous abscisic acid and 2-trans-abscisic acid in alternate bearing ‘Wilking’ mandarin trees

The relationship of abscisic acid (ABA) and 2-trans-abscisic acid (t-ABA) to alternate bearing has been examined in Wilking mandarin (Citrus reticulata Blanco) trees. Leaves, stems and buds of trees loaded with fruit (on trees) had 4.3, 6.0 and 2.2 fold higher ABA levels than the corresponding organs from off trees. Leaves had higher ABA levels than stems and buds in both on and off trees. t-ABA was non-detectable in Wilking leaf, stem and bud tissue. Amounts of t-ABA not exceeding 40% of the ABA content, were found in Shamouti and Valencia orange buds and in Wilking fruit peel.The elevated levels of ABA in on tree organs may reflect a stress imposed by the fruit overload.     

High tree alpha-diversity in Amazonian Ecuador

In a 1 ha square plot of terra firme forest at 260 m elevation in Amazonian Ecuador, all trees with diameter at breast height (dbh) 5 cm were studied. There were 1561 individuals, 473 species, 187 genera and 54 families. Of these, 693 individuals, 307 species, 138 genera and 46 families had a dbh 10 cm. This is the highest number of tree species ever recorded for a tropical rain forest sample of this size. In both dbh classes, the most species-rich families were: Fabaceae sensu lato (including Mimosaceae and Caesalpiniaceae), Lauraceae and Sapotaceae; the most species-rich genera, were Pouteria, Inga and Protium. The vertical space was partitioned among species: 166 species were found only in the 5–10 dbh cm class and were mostly sub-canopy treelets, and 307 species with dbh 10 cm were mostly large canopy trees.     

Leaf water relations and anatomy of a tropical rainforest tree species vary with crown position

Summary Leaf water potentials, osmotic properties and structural characteristics were examined in the Australian tropical rainforest tree species, Castanospermum australe. These features were compared for individuals growing in the understorey and canopy of the undisturbed forest and in an open pasture from which the forest had been cleared. Leaf water potentials during the day declined to significantly lower values in the open-grown and canopy trees than in the understorey trees. During most of the day the opengrown tree experienced the lowest water potentials. These differences were paralleled by significant differences in tissue osmotic properties. The tissue osmotic potential at full hydration was lowest in the open-grown tree (-1.80 MPa), intermediate in the canopy trees (-1.38 MPa), and highest in the understorey trees (-0.80 MPa). As a result, the degree to which high and positive turgor pressures were maintained as water potentials declined was highest in the open-grown tree, intermediate in the canopy trees, and lowest in the understorey trees. The differences in tissue osmotic properties between individuals in the three crown positions were paralleled, in turn, by differences in leaf structual characteristics. Relative to leaves of the canopy and open-grown trees, leaves of the understorey trees had significantly larger epidermal cells with thinner cell walls, larger specific leaf areas and turgid weight: dry weight ratios, and a higher proportion of intercellular air space.Abbreviations ₁ Leaf tissue water potential - _min Lowest value of ₁ during the day ( noon) - _{P=0 1} zero turgor - R Relative water content - P Tissue turgor pressure - Tissue osmotic potential - ₀ at full hydration     

Growth strategies of main trees and forest architecture of aFagus-Magnolia forest in Florida, USA

Growth strategies of six species of trees are compared and used to analyze forest architecture. They included the overstory speciesFagus grandifolia, Magnolia grandiflora, Pinus glabra andLiquidambar styraciflua, and the understory speciesOstrya virginiana andIlex opaca. The six species were abundant in Woodyard Hammock, an old-growth forest in northern Florida, USA. Height, stem diameter, crown projection and radial growth were measured in trees between 5 and 35 m tall. Three different, but non-exclusive, growth strategies were identified for the tree species: survival (Fagus grandifolia, Magnolia grandiflora, Ilex opaca), occupy open space (Fagus grandifolia, Ostrya virginiana, Ilex opaca), and reach above competitors (Liquidambar styraciflua, Pinus glabra). In two transects (0.42 ha) and one quadrat (1 ha), heights of dominant trees were used to distinguish different phases of forest development, which were mapped. In the quadrat, juvenile canopy trees in the undergrowth were mapped. The combination of presence of different developmental phases, presence of juveniles in the undergrowth, growth strategies of main tree species, and disturbance regime was used to assess forest development in the near future.Fagus grandifolia is predicted to become the main dominant species, but the frequent hurricanes open the forest canopy and provide opportunities for understory species (Ostrya virginiana andIlex opaca), and light-demanding overstory species (Liquidambar styraciflua andPinus glabra).     

The diversity of 15 ha of lowland mixed dipterocarp forest, Central Kalimantan

Fifteen hectares of primary forest in Central Kalimantan were enumerated and all trees 10 cm dbh tagged and identified to species as far as possible. Tree density, relative abundance of families and species diversity were calculated, as was a mean additive species/area curve for 1 ha and a species/area curve for all 15 ha. The Jaccard index of similarity was also calculated for the 15 plots. The 15 ha enumerated contain 8771 trees with a dbh of 10 cm, belonging to 1298 morphospecies in 56 families. On average a single plot had 583 trees and 205 species. These figures are within the upper range of species diversity for the Malesian region as a whole. Dipterocarpaceae make up 14% of all trees in the plots, closely followed by Euphorbiaceae with 13%. A surprisingly low coefficient of similarity is found between the plots, the lowest being 3% and the highest 30%. Species/area curve construction showed that the asymptote is not reached in any of the 1 ha plots or when the 15 plots are added together.     

Biological basis for the management of ‘lugs negra’ (Sarcothalia crispata Gigartinales,Rhodophyta) in southern Chile

The present paper describes growth dynamics in a natural bed of the resource luga negra (Sarcothalia crispata) in Guapilinao, southern Chile (41°57 S, 73°31 W). This resource is currently harvested and exported as raw material for the production of carrageenan. Seasonal variation in biomass, frond size, density and phenology was determined by periodic sampling. Natural recruitment was evaluated on different substrata added to the field; at the same time, substrata were inoculated under greenhouse conditions. Results showed that luga negra has seasonal growth: biomass increased from a minimum in spring to a maximum in mid to late summer. On the other hand, density was minimal in winter (200 ind. m^–2) and increased to 2000 ind. m^–2 in late spring. Peak abundance of mature tetrasporic fronds occurred in late summer, whereas that of cystocarpic fronds occurred in winter. Recruitment began in summer and extended into winter. Survival on different substrata were compared. Gametophytes had better survival rates on clam shells and 5 mm rope while tetrasporophytes had the best survival rate on clam shells and secondarily on boulders.     

The nutritional status of Picea abies (L.) Karst. across Europe,and implications for ‘forest decline’

Summary During the summer of 1986, three year-classes of foliage were sampled from approximately 30-year-old Norway spruce [Picea abies (L.) Karst.] trees at 12 sites from S. W. Germany to N. Scotland. At sites in Germany, where trees were showing symptoms of decline, samples were taken from trees with good crown condition and poor crown conditon. The distinction between good and poor was made on the basis of international protocols for defining crown density and foliar discoloration. There was a wide range in nutrient content (percent dry weight) in apparently healthy trees. Current year foliage had ranges of mean values per site: S(0.07–0.13%), N(0.9–1.4%), K(0.5–0.9%), Ca(0.2–0.7%), and Mg (0.05–0.1%). Ranges were greater for 2-year-old foliage: S(0.09–0.18%), N(1.0–1.8%), K(0.4–0.7%), Ca(0.2–1.4%), and Mg(0.03–0.09%). At sites with trees having poor crown condition, there were significantly smaller concentrations of Mg and Ca, and larger concentrations of K in 2-year-old foliage from poor trees, compared with adjacent good trees. Ratios of nutrient content were more significantly related to crown condition within sites than individual nutrients, especially in older needles. Poor crowns were associated with larger ratios of NMg, KMg, SMg, KCa and smaller ratios of SK and NK. A risk index is defined for trees showing no visible decline symptoms, based upon nutrient content and nutrient ratios, which may be useful in identifying sites liable to experience deterioration in crown condition.With the exception of one German site, where few poor trees were observed, the index increases from Scottish sites to English sites to Dutch sites to German sites. The index is empirical, and not necessarily related to potential effects of air pollution. The time dependence of foliar nutrient content may also be useful in diagnosis. At sites with trees having poor crown condition, even apparently healthy trees showed a lack of increase in calcium content with needle age, decreases in nitrogen content and very large decreases in magnesium content with needle age. The results show the importance of sampling several year classes of foliage from Norway spruce trees in determining the nutrient status of the tree.     

Effects of fire and selective logging on the tree species composition of lowland dipterocarp forest in East Kalimantan, Indonesia

Tree species composition (diameter at breast height (dbh) 10 cm) was studied in primary, selectively logged and heavily burnt forests in East Kalimantan, Indonesia. The number of trees, tree species, and the Fishers's- diversity index were determined for the first 15 years (burnt forest) and 25 years (selectively logged forest) after disturbance. Additionally the population structure of six common and typical Macaranga pioneer tree species was compared through time between selectively logged, burnt and primary forest. Both selectively logged and burnt forest showed a significant reduction in number of trees and tree species per surface area directly after disturbance. Fire especially affected dominant tree species, while for selective logging the opposite was observed. In selectively logged forest the number of trees, tree species and the Fishers's- index reached pre-disturbance levels within c. 15 years. For burnt forest, only the number of trees recovered to pre-disturbance levels. The number of tree species stayed constant after disturbance, while the Fishers's- index decreased. The six studied Macaranga pioneer tree species seedlings were present in all forest types. Their density seems to be unrelated to light levels in the forest understorey but strongly related to the number of mature parent trees. Their sapling densities were strongly related to light levels in the forest understorey. The studied Macaranga species formed an important part of both under- and over-storey in burnt forest 15 years after disturbance, while they were almost absent in the understorey and only moderately common in the overstorey of selectively logged forest.     

Slow death of Atlantic forest trees in cocoa agroforestry in southeastern Brazil

Cocoa (Theobroma cacao) is cultivated in the states of Bahia and Espírito Santo in eastern Brazil under the so-called cabruca system, where the understorey of native Atlantic forest is cleared and the canopy is thinned out to provide adequate shading for the cocoa trees. Apart from its economic and social role, the cabruca system is said to be important for the conservation of Atlantic forest biodiversity. In this paper we studied tree species richness and forest structure of cabrucas to examine the demographic health of these forests and discuss their long-term survival. Data were collected in 20 farms located alongside a 30km track of the northern margin of the Rio Doce, in northern Espírito Santo. All trees 5cm DBH were identified and their diameter was measured in 80 plots (600m²), totalling 4.8ha of sampled area. Recorded trees were also allocated to four different regeneration phases (pioneers, early secondary, late secondary and climax). The inventory resulted in 507 trees belonging to 105 species in 39 families. This species richness is much lower than in less disturbed forests located in the region. Pioneers and early secondary species dominate the cabruca forest in terms of number of species (56.2%), density (71.0%) and basal area (72.3%). The distribution of diameter frequency showed an imbalance in tree regeneration. Most trees in the range of 5–30cm DBH were pioneers (40.7%), or early secondary species (32.6%), while late secondary and climax trees were less frequent (10.2 and 16.5% of the sampled trees, respectively). The dominance of species of early regeneration phases was also observed for trees >30cm DBH (69.0% of pioneers or early secondary and 31.0% of late secondary or climax species). The results indicated that the cabruca forests are not only less diverse and less dense than secondary or primary forests of the region, but also, and more importantly, their natural succession and gap dynamics are being severely impaired. As a consequence, cabrucas present a structure where tree species of late successional phases are becoming increasingly rare while pioneers and early secondary species are becoming dominant. If current management practices of thinning and clearing of native trees are not improved, the long-term survival of these forests is questionable and their role in maintaining biodiversity in the long run is limited.     

Monosomic analysis of heading date and spikelet number in the common wheat (Triticum aestivum L.) multispikelet line ‘Noa’

Summary Genetic analysis of heading date and spikelet number was carried out in the common wheat (Triticum aestivum L.) multispikelet line Noa, by using the monosomic series of the regular line Mara. Noa's high number of spikelets was found to be controlled by a recessive major gene on chromosome 2D; a slight reduction in spikelet number was induced by another recessive gene on Noa's 7A chromosome. Noa's late heading date was found to be controlled by two recessive genes, located on chromosome 2D (a major effect) and 6B (a minor effect). The nature of the genes located on Noa's 2D chromosome and the relationship between spikelet number and heading date are discussed.     

Natural abundance of 15N in tropical plants with emphasis on tree legumes

Natural abundance of ¹⁵N ( ¹⁵N) of leaves harvested from tropical plants in Brazil and Thailand was analyzed. The ¹⁵N values of non-N₂-fixing trees in Brazil were +4.5±1.9, which is lower than those of soil nitrogen (+8.0±2.2). In contrast, mimosa and kudzu had very low ¹⁵N values (–1.4+0.5). The ¹⁵N values of Panicum maximum and leguminous trees, except Leucaena leucocephala, were similar to those of non-N₂-fixing trees, suggesting that the contribution of fixed N in these plants is negligible. The ¹⁵N values of non-N₂-fixing trees in Thailand were +4.9±2.0. Leucaena leucocephala, Sesbania grandiflora, Casuarina spp. and Cycas spp. had low ¹⁵N values, close to the value of atmospheric N₂ (0), pointing to a major contribution of N₂ fixation in these plants. Cassia spp. and Tamarindus indica had high ¹⁵N values, which confirms that these species are non-nodulating legumes. The ¹⁵N values of Acacia spp. and Gliricidia sepium and other potentially nodulating tree legumes were, on average, slightly lower than those of non-N₂-fixing trees, indicating a small contribution of N₂ fixation in these legumes.     

Diversity of forest tree species in Yanbaru,the northern part of Okinawa Island

The natural forests of Yanbaru, in the northern part of Okinawa Island, harbor many endemic and endangered birds and mammals, and are dominated by an evergreen oak, Castanopsis sieboldii. The Simpson diversity (D) and equitability index (J) were calculated using survey data on number of stems ( 4.5 cm DBH) of each species found in sample plots.Near-climax old forests (age 50 yr, without pine trees) showed high species diversity of trees, 0.92 ± 0.01 in D and 0.83 ± 0.05 in J for trees of which DBH 4.5 cm, and 0.81 ± 0.04 in D and 0.75 ± 0.05 in J for trees of DBH 10 cm.These high values are comparable to those of tropical rain forests. Although even young forests showed high species diversity, diversity indices tended to increase with forest age.The U.S. Marine Corps leases the eastern half of Yanbaru which contains most of these near-climax forests. Conservation of natural forests in this area is recommended.     

Structure and floristic composition of the lowland rain forest of Los Tuxtlas,Mexico

Physiognomy, structure and floristic composition of one hectare of lowland tropical rain forest was studied in detail at Los Tuxtlas, Mexico. Physiognomically, the Los Tuxtlas forest should be classified as lowland tropical high evergreen rain forest. The forest showed a closed canopy at 30–35 m. Of all woody, non-climbing species with a DBH1.0 cm 89.4% (94.5% of all individuals) were evergreen, 25.4% (59.5% of the individuals) had compound leaves, and over 80% of species (and individuals) had leaves in the notophyll and mesophyll size classes. The forest structure was characterized by a low density (2976 individuals with a DBH1.0 cm, 346 individuals with a DBH10.0 cm, per ha, excluding vines) with an average basal area (38.1 m², DBH1.0 cm, 34.9 m², DBH10.0 cm, per ha, excluding vines). This was attributed to the relative maturity of the forest on the study plot. The study plot contained 234 species (11 208 individuals with a height 0.5 m), of which 55.1% (34.8% of individuals) were trees, 9.4% (6.8%) shrubs, 3.4% (44.3%) palms, 20.1% (5.2%) vines, 6.8% (8.7%) herbs and 5.1% (0.3%) of unknown lifeform. Furthermore, 58 species of epiphytes and hemi-epiphytes were found. Diversity of trees, shrubs and palms with a DBH1.0 cm was calculated as Shannon-Wiener index (4.65), Equitability index (0.65), and Simpson index (0.10). The dominance-diversity curve showed a lognormal form, characteristic for tropical rain forest. The community structure was characterized by a relative dominance of Astrocaryum mexicanum in the understorey, Pseudolmedia oxyphyllaria in the middle storeys, and Nectandra ambigens in the canopy. Species population structures of 31 species showed three characteristic patterns, differentiated by recruitment: continuously high, discontinuously high, and continuously low recruitment. Height/diameter and crown cover/diameter diagrams suggested a very gradual shift from height growth to crown growth during tree development. Forest turnover was calculated as 138 years. Compared to other tropical rain forests the Los Tuxtlas forest had 1. similar leaf physiognomical characteristics, 2. a lower diversity, 3. a lower density, 4. an average basal area, and 5. a slow canopy turnover.     

Microsatellite markers in the hexaploid Prunus domestica species and parentage lineage of three European plum cultivars using nuclear and chloroplast simple-sequence repeats

In a previous study, cDNA microsatellite markers were described in apricot (Prunus armeniaca L.). Specific PCR primers were designed to amplify the microsatellite-containing regions from genomic DNA in different Prunus species. In the present work, cDNA microsatellite markers were developed in the hexaploid Prunus domestica L. species and polymorphism was ascertained in a segregating plum population. Co-dominant mendelian segregation of alleles was demonstrated and microsatellite polymorphism displayed up to 6 alleles per SSR locus per individual. Parentage lineage of three full-sib European plum cultivars (cv. Cacanska najbolja, Cacanska rana and Cacanska lepotica) was reconstructed by the analysis of the above nuclear SSR markers, completed by four chloroplastic microsatellite loci. The six most informative nuclear loci enabled discrimination between the three Cacak cultivars and unrelated individuals as well as the previously proposed parents, Wangenheim and Pozegaca. Data obtained support previous evidence that these cultivars originated from the Stanley cultivar. However, SSR analysis finally excluded Wangenheim as the other possible parent. Based on the results obtained with nuclear and chloroplast SSR loci, we propose the origin of those three Cacak cultivars in a cross between Stanley as the mother plant and Ruth gerstetter as the pollinator. Furthermore, we demonstrate the utility of these apricot SSR markers for genotype fingerprinting of the hexaploid plum cultivars.     

Uptake and metabolism of benzyladenine during shoot organogenesis in Petunia leaf explants

Benzyladenine (BAP) uptake and metabolism were characterized during the key stages of shoot organogenesis in leaf explants of Petunia MD1. Using leaf explant transfer experiments, it was shown that exposure to 2.2 M BAP for 6, 8 or 10 days induced shoot formation on 27, 80 and 100% of the explants respectively, with a concomitant increase in the number of shoots per explant. BAP uptake and metabolism were characterized in leaf explants after 1, 3, 6 or 10 days exposure to [³H]BAP or 10 days exposure plus an additional 2 days on basal medium (10+2). BAP and 9--D-ribofuranosyl-BAP ([9R]BAP) were detected at days 1 and 3 only. Therefore, the BAP free base was not detectable during the shoot induction period between days 6 and 10, as defined by leaf transfer experiments. The BAP ribotide pool was largest on day 1 and decreased to day 10+2. It is possible that the BAP ribotide pool provided either the active cytokinin itself or acted as a short-term storage form for the active cytokinin in petunia shoot organogenesis. Other metabolites detected in petunia leaf tissue included 7--D-glucopyranosyl-BAP ([7G]BAP), 9--D-glucopyranosyl-BAP ([9G]BAP) and an unidentified metabolite C.Abbreviations BAP benzyladenine - [7G]BAP 7--D-glucopyranosyl-BAP - [9G]BAP 9--D-glucopyranosyl-BAP - [9R]BAP 9--D-ribofuranosyl-BAP - [9R-5P]BAP 5-monophosphate of [9R]BAP - [9R-5PP]BAP 5-diphosphate of [9R]BAP - [9R-5PPP]BAP 5-triphosphate of [9R]BAP - TEA Triethylamine This research was supported in part by NSF Grant DCB-8917378 to J.D.C. and USDA-CRGO Grant 89-37261-4791 to T.J.C.     

Gene structure of the ‘large’ sialidase isoenzyme fromClostridium perfringens A99 and its relationship with other clostridialnanH proteins

Clostridium perfringens possesses two sialidase isoenzymes of different molecular weight. Almost 90% of the gene encoding the large form was found on a 3.1 kb chromosomal fragment (Sau3AI) of strain A99 by hybridization with probes developed from the N-terminal protein sequence and from commonly conserved sialidase motifs (Asp-boxes), whereas the remaining 3-terminal part was detected on a 2.1 kb fragment (Hind III) of chromosomal DNA. After combination of both fragments, the resultingE. coli clones expressed sialidase activity, the properties of the recombinant sialidase corresponding with those of the wild type enzyme. The entire chromosomal fragment of 3665 bp encompasses the complete sialidase gene of 2082 bp corresponding to 694 amino aids, from which a molecular weight of 72956 for the mature protein can be deduced. The first 41 amino acids are mostly hydrophobic and probably represent a signal peptide. The sialidase structural gene follows a non-coding region with an inverted repeat and a ribosome-binding site. Upstream from the regulatory region, another open reading frame (ORF) was detected. The 3-terminus of the sialidase structural gene is directly followed by a further ORF of unknown function, which possibly encodes a putative permease or the acylneuraminate pyruvate-lyase involved in sialic acid catabolism. The primary structure of the large isoenzyme is very similar to the sialidase ofClostridium septicum (55% identical amino acids), whereas the homology with the small form of the same species is comparatively low (26%).     

Variability in the 11S globulin fraction of seed storage proteins ofHelianthus (Asteraceae)

The seed storage globulins from sixHelianthus and four hybrids were studied using mono and bidimensional gel SDS electrophoresis (+ 2 mercaptoethanol). The polypeptide composition of each subunit was determined. Different pairs are specifically expressed according to the species studied. Three typical patterns were discriminated. All the studied species exhibit five subunits: two of them are expressed in all the species (₁₁ and ₂₂). The subunit corresponding to the ₁₁ pair is present inH. petiolaris and in the three populations ofH. annuus studied. The _2b2 pair is common toH. annuus andH. argophyllus. H. petiolaris presents two specific _2a2 and ₄₄ pairs andH. annuus a specific ₃₃ pair. InH. argophyllus _{11 33} or ₄₄ are never observed but are replaced by ₁₃ and ₃₁ pairs. Some globulins, poorly represented, are of forms but present chains of higher molecular weights (in the range 54–56 kDa). Expressing variations in the banding patterns between these species by the use of a similarity index reveals complete identity between the three populations ofH. annuus. Identity between the twoH. petiolaris studied is also observed.H. annuus andH. argophyllus appear to be closer to each other thanH. petiolaris concerning the seed storage globulins.     

Synthesis of N-linked pentasaccharides with isomeric glycosidic linkage

As part of a program to explore the structural requirement of N-glycans in the carbohydrate-mediated biological interactions, N-linked pentasaccharide core structure was stereochemically modified in terms of glycosidic linkage. Three isomers, -D-Man-(13)-[-D-Man-(16)]--D-Man-(14)--D-GlcNAc-(14)--D-GlcNAc-L-Asn, -D-Man-(13)-[-D-Man-(16)]--D-Man-(14)--D-GlcNAc-(14)--D-GlcNAc-L-Asn, and -D-Man-(13)-[-D-man-(16)]--D-Man-(14)--D-GlcNAc-(14)--D-GlcNAc-L-Asn, were synthesized. Synthesis of the pentasaccharide with natural linkage is also described.     

The mitochondrial membrane potential (deltapsi(m)) in apoptosis; an update

Mitochondrial dysfunction has been shown to participate in the induction of apoptosis and has even been suggested to be central to the apoptotic pathway. Indeed, opening of the mitochondrial permeability transition pore has been demonstrated to induce depolarization of the transmembrane potential (_m), release of apoptogenic factors and loss of oxidative phosphorylation. In some apoptotic systems, loss of _m may be an early event in the apoptotic process. However, there are emerging data suggesting that, depending on the model of apoptosis, the loss of _m may not be an early requirement for apoptosis, but on the contrary may be a consequence of the apoptotic-signaling pathway. Furthermore, to add to these conflicting data, loss of _m has been demonstrated to not be required for cytochrome c release, whereas release of apoptosis inducing factor AIF is dependent upon disruption of _m early in the apoptotic pathway. Together, the existing literature suggests that depending on the cell system under investigation and the apoptotic stimuli used, dissipation of _m may or may not be an early event in the apoptotic pathway. Discrepancies in this area of apoptosis research may be attributed to the fluorochromes used to detect _m. Differential degrees of sensitivity of these fluorochromes exist, and there are also important factors that contribute to their ability to accurately discriminate changes in _m.     

The relation between eardrum failure and blast-induced pressure variations

During a series of field and laboratory experiments designed to study overall blast effects, incidental observations were made of the ears of more than 490 animals to determine eardrum failures associated with exposure to atypical and typical blast wave forms. Animals positioned inside structures were exposed to a variety of atypical blast waves, whereas those located inside shock tubes or in the open, when high explosives were detonated, were exposed to fairly typical wave forms. When the incidence of eardrum rupture is related to the various elements of the measured pressure-time curves, the association is not the same for the two types of wave shapes. Besides suggesting that tolerance is higher for slow-than for fast-rising wave forms, the findings demonstrate a wide variability in the magnitude of the overpressures required to rupture the eardrum. Within the limits of the data available, the quantitative differences are noted and discussed with emphasis on the apparent wide variability in tolerance and a proposed explanation for this finding. Although the results are limited strictly to the mammalian species studied, it is likely that the eardrum of man also is sensitive to the shape and character, as well as the magnitude and duration of the blast wave. The data are useful to military and civilian physicians, industrial otologists and all other health and safety personnel including those who have research interests in establishing quantitative dose-response criteria for individuals exposed to blast-induced variations in pressure.Deceased.