At this stage, plant tissue may have fewer physical barriers to exogenous treatments, such as gases (carbon dioxide, ozone,
etc.) or chemicals (growth regulators, herbicides, etc.) or even pathogens that might be present in the ex vitro environment.
Plant hormones such as absicic acid (ABA)
have been applied during this period to increase plant endurance
for further development, (Pospíŝilová et al., 1998;
2007), thus suggesting that early application of hormones
might be recommended