Patrick Echlin

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The final stages of Helleborus pollen-grain ontogeny, which culminate in maturation and germination of the grain, have been investigated at the ultrastructural level. Following the deposition of primary and secondary exine, and during the early stages of intine formation, the microspore passes through a vacuolate phase, in which the cytoplasm appears devoid(More)
Low temperature scanning electron microscopy is useful for morphological and analytical studies both in situations where low temperature techniques are used during specimen preparation and where low temperature stages are used for specimen examination and analysis. Examples are given of different low temperature specimen preparation techniques and how they(More)
X-ray microanalysis of frozen-hydrated tissue sections permits direct quantitative analysis of diffusible elements in defined cellular compartments. Because the sections are hydrated, elemental concentrations can be defined as wet-weight mass fractions. Use of these techniques should also permit determination of water fraction in cellular compartments.(More)
Behnke (1963) has recently described a helical arrangement of ribosomes in differentiating cells of the small intestine of the rat fetus, and Waddington and Perry (1963) have found the same structures in the muscle cells of Rana pipiens embryo. In the course of an investigation into the development of pollen in Ipomoea purpurea (L.) Roth, a similar(More)
There are several limitations to the low-temperature techniques which are currently being used for the preparation, examination and analysis of biological and organic samples by means of high-energy beam instrumentation. The low thermal conductivity of samples and the inadequacy of rapid cooling techniques means that, with the exception of thin-film(More)
l The organism was sent to me by Dr. L. Provasoli of the Haskins Laboratory, New York, as a species of Synechococcus. It was subsequently identified as Anacystis montana fa. minor (Wille) Drouet and Daily (5), (6) by Dr. F. Drouet of the Academy of Natural Sciences, Philadelphia. it was found that the outermost layer of the cell boundary is convoluted into(More)