About these sowns, I see that something is said in addition about the precise difference between John the Baptist and the other three ''sowns''.
The sown that allegorizes John the Baptist is never transformed in a plant.
While the ''sown'' Peter, the ''sowns'' James and John and the ''sown'' Paul are destined to grow so that they become a plant. But only the ''sown'' Paul bears ''fruit''.
My view is that the action of becoming a ''plant'' means ''to have seen Jesus''.
Therefore John the Baptist dies without really see and listen Jesus.
There is another point of interest about the ''sown'' Peter:
(Mark 4:5-6)Other seed fell on rocky ground, where it did not have much soil, and it sprang up quickly, since it had no depth of soil. And when the sun rose, it was scorched; and since it had no root, it withered away.
The ''sun that rose'' is generally symbol of resurrection (cfr the song of roaster during the Peter's denial) but also of death, given Mark 15:33 :
The ''plant'' Peter dies when ''the sun rose'': when the Messiah is crucified, a fact not accepted by Peter (cfr Mark 8:32-33).When it was noon, darkness came over the whole land until three in the afternoon.
The ''sown'' James and John sons of Zebedee are allowed to become ''plants'' (they will share the Eucharist) but they cannot have ''fruit'', i.e., disciples among the gentiles (only the ''sown'' Paul can).
Therefore ''Mark'' is describing the origins of the movement, by the Parable of Sower. The parable explains why John the Baptist is seen as essential to that origin, even if it is admitted that John didn't see the angel Jesus. John could become a Christian apostle - could see the angel Jesus the first time in a hallucination - but he was killed (''eaten by birds'') BEFORE that he could do so. Therefore the fate of John - and of all the ancient prophets - was to prophetize the Christ without having never the privilege of seeing him.
Different is the fate of Peter and Pillars: they are more worthy of condemnation, because they saw the angel Jesus - via hallucinations - but they didn't follow Paul in Galilee of gentiles.
It is interesting that with Mcn, Luke and Matthew we listen another different final about John the Baptist: in later Gospels, John is given really the possibility of listening about the news and prodigia about Jesus, but he becomes blind and delusional (just as the 12 in Mark: the hand of Marcion, here) - in Mcn=proto-Luke - or he becomes a converted Christian in extremis (in the proto-catholic Matthew).
Therefore only Marcion and ''Matthew'' (author) had real interest to make John conscious of the the prodigia made by Jesus, in order to describe his reaction to these prodigia:
1) negative reaction, in Mcn.
2) positive reaction, in Matthew.
Mark precedes both Marcion and ''Matthew'' because his goal is only to coopt the prestige of John the Baptist in order to explain why the prophets - even the contemporary prophets of the Messiah, if someone was there - didn't know the Messiah Jesus.