The outer part of the exine, which stains positively with basic fuchsin in optical microscopy and has higher electron density in conventionally prepared TEM sections.
Source:
http://www.mobot.org/MOBOT/research/APweb/
Comment
Note that ectexine is distinguished on staining properties; compare with 'sexine ; GO:0043673'. See also 'endexine ; GO:0043671'.