Those who have read the pre-Pacelli texts for Palm Sunday will have noticed that olive branches feature just as much as palm branches. This is hardly surprising. The Lord rode in from 'Mount Olivet'; in the Greek to oros ton elaion (S Augustine proposed translating this as 'the Mount of Chrism'). So when we are told that the crowd cut (ekopton) branches from the trees, we might well conclude that olive branches are largely meant.
These texts allude to the Olive sprig which Noe (Noah) received from his enterprising dove; and explain to us that "surculi olivarum spiritualem unctionem advenisse quodammodo clamant" -- the twigs cry out that a spritual anointing has arrived.
Indeed it has.
Because this symbolism of the Olive makes a link with the Consecration of the Chrism, traditionally associated with Maundy Thursday. That is when the threee oils are blessed or consecrated by the Bishop, who used to concelebrate this Consecration with twelve chasubled presbyters. In the good old truly collegial days before the Council, all twelve of these priests breathed the Spirit, which they collegially share with their Pontiff, upon the Oil. I suppose the innovators had to find room in the Rite for their spiffing new idea of having all the prebyterium renewing its 'ordination vows'.
This Chrism will be used in the rites of Christian initiation at the Easter Vigil, to confer the Sacrament of Confirmation (or Consignation). Traditionally, this Oil has been seen as so sacred that S Cyril of Jerusalem (whom Gregory Dix once described as 'very extreme') regarded its consecration as being parallel with the transsubstantiation of the Eucharistic Elements, with the result that it 'became' (ginomenon) the charisma of Christ and 'effective of His Godhead' (tes autou theotetos energetikon). (When this Catechesis was incorporated into the Liturgia Horarum, that paragraph was eliminated!!) Among some Byzantines, the confection of the Chrism is restricted to Patriarchs. One can see why.
One more section will complete this series.