Figure 1.

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).