Surely, the composer intended a pronounced rallentando on the latter half of the bar, and a carrying of the voice by a Portamento to the last note.
"Style in Singing"
W. E. Haslam
Most often, however, his voice puts me in mind of the cardinal grosbeak's; his voice, and perhaps still more his cadence, and especially his practice of the Portamento.
"Birds in the Bush"
Bradford Torrey
His lyricism is most human, while the Portamento, the slides, trills and indescribably subtle turns-are they not of the violin?
"Chopin: The Man and His Music"
James Huneker