SUMMARYIn an examination of possible harmful effects to plants caused by spraying leaves with inert dust suspensions it was shown that Stockalite (kaolin), talc, silica or Tiona W.D. (titanium oxide), suspended in water and sprayed on excised leaves of three species, significantly (P≯ 0·05) increased water loss and penetration of gaseous ammonia; these increases were not caused by soluble chemicals in the sprays, but depended on intimate contact of the dust particles with the epidermis. With a given dust, epidermal permeability increased with increasing concentration and with decreasing size of particles. The increased permeability persisted for at least 4 weeks and was unaltered by partial removal of deposits; deposits on bean leaves caused more visible damage in dry than in humid air. Water losses from sprayed adaxial and abaxial leaf surfaces were similar, but more was lost when deposits dried on turgid leaves than when they dried on flaccid ones.Spraying potted Coleus plants with a Stockalite suspension increased transpiration and, in one test, decreased the fresh weight of the Coleus shoots.

SUMMARY Techniques were tested to ascertain the best method for preparing the surfaces of delicate plant cuticles for microscopic examination at magnifications not exceeding 10,000. Using scanning electron microscopy, comparative examinations were made of cuticles of fresh material, ambient dried, freeze dried, critical point dried, and frozen material kept at low temperature. Micrographs were compared with material examined using light microscopy which acted as a control at low magnification. Cuticles of the leaves of runner bean, Coleus and the petals of Nicotiana, showed best surface preservation and least wrinkling when frozen, held at low temperature, and examined on a cryostage.

Summary The cuticle surfaces of fresh, uncoated petals of Nicotiana alata Link & Otto and leave of Phaseolus coccineus L., Coleus blumei Benth. and Dactylis glomerata L. were examined in a canning electron microscope using a range of accelerating voltages, beam currents and recording scan times. The best micrographs of undamaged and unwrinkled cuticles, taken at magnifications ranging from 500 to 5000. were‐obtained using an accelerating voltage of 10kV, a low beam current and a recording scan time of 40 s. Fixation of the cuticles with osmium tetroxide vapour neither reduced charging nor improved preservation. The examination of the fresh uncoated cuticles proved an acceptable check or control for other methods used to prepare the auricles for scanning elecrron microscopy.

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