It has been reported
that plum growth parameters (volume and polar, suture and
cheek diameters, and fruit weight) follow a double sigmoid
pattern, which is typical for Prunus species (Valero and Serrano,
2010). Four distinct stages (S1–S4) could be established in this
curve: S1 is the first exponential growth phase and characterised
by cell division and elongation, S2 shows little or no
fruit growth but the endocarp hardens to form a solid stone,
S3 is the second exponential growth phase due to cell enlargement,
while in S4 the fruit ripening or climacteric stage occurs