Whittaker’s plant collecting activities began to decline around 1863, around the time his botanical partner, Henry Harpur Crewe, moved away to become the Rector of Drayton Beauchamp in Buckinghamshire.
Aktivitas mengoleksi tanaman Whittaker mulai menurun sekitar tahun 1863, ketika itu rekanan botanisnya, Henry Harpur Crewe, pindah untuk menjadi Rektor Drayton Beauchamp di Buckinghamshire.