Automatic motion of Averrhoa Bilimbi

— An instance of leaf motion which I believe to have some physiological interest.

The leaflets of Averrhoa Bilimbi are depressed by their own act, with more or less frequence during the day, to nearly the position of sleep, but so slowly in succession that the phenomenon very easily escapes observation.² The motion is steady and continuous up to completion of the movement—not spasmodic as in the case of Desmodium gyrans.³ Usually there is only one leaflet of a leaf in downward motion at the same time, the next to follow is generally the one most nearly opposite, or the one next on the same side. From slight observation there is no evident law in the order of succession but the leaflets of a leaf are never all down at the same time. The downward movement is quickly performed but the return motion is so slow as to imperceptable. The activity of the plant appears to be chiefly influenced by the degree of light. During bright weather if the plants are shaded there is little or no movement, but on the shading being drawn up there immediately commences a lively depression of the leaflets

Averrhoa Bilimbi is subject to the condition of sleep and is sensitive to mechanical irritation, with also the automatic motion above mentioned

These phenomena have not perhaps been together recorded of the same plant. Desmodium gyrans having the automatic movement is not appreciably influenced by mechanical irritation, Mimosa pudica having a high degree of “sensitiveness” is without the automatic movement, while both are subject to the condition of sleep.⁴ Desmodium gyrans though less active during the night, even then continues the gyration of its small leaflets, Averrhoa on the other hand is only active during the day and is then greatly affected by the degree of light

R. Irwin Lynch | Royal Gardens | Kew