The developmental stages of cucumber cotyledons.
Stages through which the cotyledons pass from imbibition, through early
expansion growth to maturity, early to late senescence, and finally
cell death are defined as days after seed imbibition (DASI) on the
basis of chlorophyll content and organ color. On d 3, cotyledons are
green and just starting their expansion growth phase (stage I), then
they undergo a period of expansion until they are mature around d 15
(stage II and III). By d 28, the cotyledon retains 65% of mature
cotyledon chlorophyll content (stage IV); this is termed the early
senescent stage. By d 36, the cotyledon retains 35% of mature
cotyledon chlorophyll content (stage V); this is termed the
mid-senescence stage. The cotyledon subsequently becomes yellow
in late senescence (stage VI). Following the yellow stage the cotyledon
enters a brief stage where it turns brown and becomes crispy (stage
VII).