SEM studies of the morphology and chemistry of polar ice

Determining the microphysical location of impurities in natural ice from the polar regions is necessary for understanding the physical properties of ice and for assuring the integrity of ice core records. SEM, using a cold stage and X-ray microanalytical techniques, has proved to be the most powerful method so far for undertaking such work. Methods are adapted from those used to study frozen hydrated biological material. Sublimation within the cryo-chamber is often needed in order to concentrate impurities onto a plane, but this can lead to artifacts that must be recognized. Over 100 samples from different depths and sites in Greenland and Antarctica have been examined. Typical physical features, including air bubbles, clathrate hydrates of air, and dust particles are identified. The dust is found preferentially at grain boundaries in some samples; by pinning the boundaries, it can slow grain growth. Of the soluble material, chloride seems to be found most frequently in the ice lattice. Other impurities are found at grain boundaries, and only when the bulk concentration exceeds a threshold, at triple junctions. These findings give new insights into processes determining the physical properties of ice samples and of ice sheets, and new impetus for theoretical studies of the energetics that lead to this distribution.     

A new Δ7-polyunsaturated fatty acid in taxus spp. Seed lipids, dihomotaxoleic (7,11–20∶2) acid

A previously undescribed fatty acid, all-cis 7, 11–20∶2 (dihomotaxoleic acid, DHT), has been characterized by gas chromatography-mass spectrometry as being present (approximately 0.1%) in seed oils of two Taxaceae containing high levels (11–16%) of taxoleic acid (all-cis 5,9–18∶2). This compound was absent from oils of 10 other conifer genera, as well as from one member of Taxaceae containing very low amounts of taxoleic acid, suggesting that DHT is a taxoleic acid elongation product.     

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Search for new industrial oils. XIV. Seed oils of labiatae

Seed of 194 species in 56 genera of Labiatae, representing six of the eight subfamilies, were analyzed for oil and protein and for fatty acid composition of the oil. The oils are diverse and include some that contain up to 70% oleic acid, 79% linoleic acid, or 72% linolenic acid. An allenic function occurs in a third of the samples from the subfamily Stachyoideae and in the one sample analyzed from the Prasioideae. A method for determining the allene was devised. Oils fromTeucrium species containtrans unsaturation in unidentified components. Oils from twoLamium species have both allenic andtrans unsaturation. Two species ofThymus appear to produce hydroxy acids. Presented in part at the AOCS Meeting, Houston, April 1965. No. Utiliz. Res. Dev. Div., ARS, USDA. Crops Research Div., ARS, USDA.     

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Fatty acid composition of pinaceae as taxonomic markers

Following our previous review on Pinus spp. seed fatty acid (FA) compositions, we recapitulate here the seed FA compositions of Larix (larch), Picea (spruce), and Pseudotsuga (Douglas fir) spp. Numerous seed FA compositions not described earlier are included. Approximately 40% of all Picea taxa and one-third of Larix taxa have been analyzed so far for their seed FA compositions. Qualitatively, the seed FA compositions in the three genera studied here are the same as in Pinus spp., including in particular the same Δ5-olefinic acids. However, they display a considerably lower variability in Larix and Picea spp. than in Pinus spp. An assessment of geographical variations in the seed FA composition of P. abies was made, and intraspecific dissimilarities in this species were found to be of considerably smaller amplitude than interspecific dissimilarities among other Picea species. This observation supports the use of seed FA compositions as chemotaxonomic markers, as they practically do not depend on edaphic or climatic conditions. This also shows that Picea spp. are coherently united as a group by their seed FA compositions. This also holds for Larix spp. Despite a close resemblance between Picea and Larix spp. seed FA compositions, principal component analysis indicates that the minor differences in seed FA compositions between the two genera are sufficient to allow a clear-cut individualization of the two genera. In both cases, the main FA is linoleic acid (slightly less than one-half of total FA), followed by pinolenic (5,9,12-18:3) and oleic acids. A maximum of 34% of total Δ5-olefinic acids is reached in L. sibirica seeds, which appears to be the highest value found in Pinaceae seed FA. This apparent limit is discussed in terms of regio- and stereospecific distribution of Δ5-olefinic acids in seed triacylglycerols. Regarding the single species of Pseudotsuga analyzed so far (P. menziesii), its seed FA composition is quite distinct from that of the other two genera, and in particular, it contains 1.2% of 14-methylhexadecanoic (anteiso-17:0) acid. In the three genera studied here, as well as in most Pinus spp., the C₁₈Δ5-olefinic acids (5,9-18:2 and 5,9,12-18:3 acids) are present in considerably higher amounts than the C₂₀Δ5-olefinic acids (5,11-20:2 and 5,11,14-20:3 acids).