David Hoekman

Ecological wood anatomy of the woody southern Californian flora.

Wood of 207 species, representing all 178 woody genera of the Munz flora of southern California, was studied by means of sections and macerations. Data were gathered on features relating to the conducting system: number of vessels per mm2, diameter of vessels, length of vessel elements, number of bars per perforation plate, presence of true tracheids, vasicentric tracheids, vascular tracheids, helical sculpture, and growth rings. The occurrence of these features is analysed both with respect to each other and to ecological groupings and habit groupings. Statistically significant data permit ecological groupings to demonstrate degree of xeromorphy in wood features. Xeromorphy is indicated by more numerous vessels per mm2, narrow vessels, shorter vessel elements, presence of vasicentric tracheids or vascular tracheids, presence of helical sculpture on vessel walls, and presence of well-marked growth rings (growth rings are common in moist habitats because in southern California these are also montane and therefore cold in winter). All of these appear to have developed in many phylads independently. Vessel element length appears to change less rapidly, at least in some phylads (those with true tracheids) than the other features. Presence of scalariform perforation plates and of true tracheids is interpreted as relictual; scalariform plates occur virtually only in mesic habitats and in a small number of species. True tracheids, although relictual in nature, have been preferentially preserved because of the value of their enormous safety. Groups without true tracheids have evolved vasicentric tracheids or vascular tracheids (the three types are mutually exclusive) to a high degree. By deducting the species with true and vascular tracheids, one finds that 100% of the alpine shrubs, 77% of the desert shrubs, and 75% of the chaparral shrubs which could possibly have evolved vasicentric tracheids actually have them. These are the three ecological groupings which have vasicentric tracheids not only in southern California, but other areas of the world as well. Tracheid presence (and to a lesser extent vasicentric tracheid presence) forestalls vessel grouping, but in tracheid-free groups vessel grouping is a highly adaptive strategy for xeromorphy. One can rank xeromorphic connotation of qualitative features on the basis of data herein: growth rings are the most common numerically, followed by helical sculpture, vasicentric tracheids, and vascular tracheids. Vasicentric tracheids, like true tracheids, tend to occur in evergreen shrubs whereas vascular tracheids tend to be related to drought-deciduous shrubs. Among quantifiable features, number of vessels per mm2 changes more rapidly than vessel diameter. Scalariform perforation plates, true tracheid presence, and long vessel elements are associated with each other statistically . By entering number of woody species for each genus in the flora and performing appropriate computations, a figure for each feature is projected on the basis of the 512 woody species of southern California. This pro-rated figure shows that phylads with any of the mechanisms cited as signifying xeromorphy speciate much more rapidly than do the phylads with mesomorphic wood features.

The expanding role of quantitative structure-activity relationships (QSAR) in toxicology

Quantitative structure-activity relationships (QSAR) have found wide use in correlating the bioactivity of all kinds of organic compounds with all kinds of biological entities. So many QSAR have been published that it is time for a new phase of study, that of comparative QSAR. From our current database of about 6000 QSAR illustrative examples are discussed.

On the Role of Polarizability in Chemical−Biological Interactions

This report considers the importance of electronic effects in their role in the QSAR of chemical-biological interactions. The problem of accounting for polarizability effects in ligand-substrate interactions is discussed in terms of molecular polarizability (MR) and NVE (number of valence electrons) using additive values for valence electrons. The two approaches give essentially the same result in examples of frog nerve toxicity and examples of nerve toxicity with rabbits and cockroaches. The point is made that no matter how one approaches QSAR, electronic interactions must be considered if we are to begin to develop a science of chemical-biological interactions.

The partition of compounds from water and from air into wet and dry ketones

Literature data on partitioning of compounds from the gas phase to ketones and from water to ketones has been collected and analyzed through the Abraham solvation equations. It is shown that for partition into both dry and wet ketones the main solvent factors that aid partitioning into the ketones are the polarizability/dipolarity, hydrogen-bond basicity and hydrophobicity (size) of the ketones. Reliable equations have been established for partitioning from the gas phase and from water to dry acetone, dry butanone, dry cyclohexanone and to wet methyl isobutyl ketone. It is further shown that partitioning into dry butanone and dry cyclohexanone leads to different equations than partitioning into the wet solvents, and that data on partitioning into the wet and dry ketones cannot be combined.

Partition of compounds from water and from air into the wet and dry monohalobenzenes

Values of the partition coefficient from the gas phase (Ks) and from water (Ps) to the monohalobenzene solvents have been collected for fluorobenzene (21 solutes), chlorobenzene (212 solutes), bromobenzene (126 solutes) and iodobenzene (65 solutes). It is shown that for the wide range of solutes studied, partitions into the dry and wet (water-saturated) solvents are essentially the same, and that equations can be constructed that include data on both dry and wet solvents. Using the Abraham equations, that contain a maximum of five descriptors, statistically satisfactory equations are obtained for log Ks and log Ps with estimated predictive standard deviations of around 0.20 log units. The coefficients in the Abraham equations for the four halobenzene solvents are surprisingly similar and except for the s-coefficient, which reflects the solvent dipolarity/polarisability, are also similar to the coefficients for partition into toluene.

Water–Solvent Partition Coefficients and Δ Log P Values as Predictors for Blood–Brain Distribution; Application of the Akaike Information Criterion

It is shown that log P values for water-alkane or water-cyclohexane partitions, and the corresponding Delta log P values when used as descriptors for blood-brain distribution, as log BB, yield equations with very poor correlation coefficients but very good standard deviations, S from 0.25 to 0.33 log units. Using quite large data sets, we have verified that similar S-values apply to predictions of log BB. A suggested model, based on log P for water-dodecane and water-hexadecane partition coefficients, has 109 data points and a fitted S = 0.254 log units. It is essential to include in the model an indicator variable for volatile compounds, and an indicator variable for drugs that contain the carboxylic group. A similar equation based on water-chloroform partition coefficients has 83 data points and a fitted S = 0.287 log units. We can find no causal connection between these log P values and log BB in terms of correlation or in terms of chemical similarity, but conclude that the log P descriptor will yield excellent predictions of log BB provided that predictions are within the chemical space of the compounds used to set up the model. We also show that model based on log P(octanol) and an Abraham descriptor provides a simple and easy method of predicting log BB with an error of no more than 0.31 log units. We have used the Akaike information criterion to investigate the most economic models for log BB.

Wood Anatomy of Staphyleaceae: Ecology, Statistical Correlations, and Systematics

Summary Wood of Staphyleaceae is characterized by vessels which are mostly solitary; vessel elements are long with scalariform perforation plates (mostly more than 20 bars per plate) and with scalariform, opposite, or alternate lateral wall pitting. Imperforate tracheary elements range from fiber-tracheids with fully bordered pits somewhat less dense than those of tracheide (Euscaphis, Staphylea, Turpinia) to fiber-tracheide with reduced borders on pits (Huertea) to libriform fibers (Τapiscia) . Axial parenchyma is mostly abaxial, with tendencies towards vasicentric scanty and ray-adjacent cells and only a few diffuse cells. Rays are both multiseriate and uniseriate. Heterogeneous Type IIA. The multiseriate portion of multiseriate rays is often not sheathed with upright cells and consists of procumbent cells which often have bordered pits on radial walls. Rhomboidal crystals, tyloses, and dark-staining amorphous deposits are found in some but not all species. Quantitative features show wood of Staphylea to be less markedly mesomorphic than that of the other genera, a fact perhaps related to winter cold. The Mesomorphy index is held to be more useful in analysis of dicotyledon woods and in predicting relationship with ecology than a conductivity formula, because it runs parallel to ecological gradients, takes into account vessel element length (apparently related to embolism localization), and represents degrees of relinquishment of safety as woods become more mesomorphic. Statistical correlation among wood features of Staphyleaceae show vessel element length related to imperforate tracheary element length and to ray height because all of these are linked to fusiform cambial initial length. Correlation between vessel diameter and vessel element length is slightly weaker, as is inverse correlation between vessel diameter and vessel density (where packing constraints tend to enforce a correlation). The genera of Staphyleaceae can be easily characterized by wood anatomy features such as growth ring presence or absence, perforation plate bar number, presence of helical sculpture within vessels, type of imperforate tracheary element, presence of septa in fibers (in which case axial parenchyma is absent), ray dimensions, tylosis occurrence, and crystal presence. Wood of Staphyleaceae most closely resembles that of some Cunoniales (Saxifragales), and resembles that of Sapindales somewhat less.