The external morphology, internal structure and stainability for protein of orbicules inBetula pendulaare examined by SEM and TEM. The pollen and the orbicule walls stain moderately for protein. The protein is localized mainly at the pollen aperture, in a thin layer between the exine and the intine and in the core and on the surface of the orbicules. The nitrocellulose membrane test indicates possible allergenicity of the orbicules as well as of the pollen. Since the orbicules ofBetula pendulaare 2#x2013;4 um in diameter, they can pass through the bronchiole of the lungs and cause bronchial asthma.
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