As I understand it, the "cress" you buy in punnets frome the
greengrocer's is not cress but mustard.
When I used to grow it you bought a packet of each and sowed the
cress a few days before the mustard because the latter germinates more
quickly.
Mustard seeds are pale and round. Cress seeds are a conker colour and
smaller. When they get wet they develop a slimy coating.
I have never grown cress beyond the seedling stage to see what
develops.


Pam in Bristol