SENSITIVE PLANTS 
SENSITIVE PLANTS 
Natural Order Leguminosjc. Genus Mimosa, 
Mimosa (Latin, mimos, a mimic; from the leaves of some species 
mimicking animal movements when touched). A large genus (about 
230 species) of herbs chiefly, and a few tall climbing shrubs and trees. 
They are distinguished by their twice-pinnate leaves—that is, the leaf is 
broken up into several pinnae, or wings, each of which is again divided 
into a number of small leaflets. The flowers are small and stalkless, 
gathered into small roundish heads, or cylindrical spikes. The stamens 
are definite in number, never more than twice the number of petals; and 
the pod is of a peculiar pattern, being jointed between each two seeds, 
and the valves separating from the rim, which is left attached to the 
stalk. The species are almost all tropical, mostly American, a few only 
being indigenous to Africa and the East Indies. 
The few species of Mimosa that are cultivated in our 
greenhouses owe their presence there not to any brilliance 
of colour or choiceness of perfume, but to an interesting irritability of 
the leaflets. This phenomenon led to the introduction of M. pudica from 
Brazil in 1638, and the less sensitive M. sensitiva ten years later. All 
the species are sensitive to light, and in its absence close down their 
leaves towards the stem. M. pudica, in addition, is so irritable that 
if any portion of the plant is touched, the secondary leaflets contract 
closely together, so that a plant which a minute before was well- 
clothed with foliage, appears to be leafless. Much attention has been 
paid, by a number of careful investigators, to these peculiar move¬ 
ments; but with little result beyond ascertaining that the cells on 
opposite sides become alternately turgid by the absorption of fluid 
from each other, and so produce a different attitude in the leaves 
and leaflets. The mere sensitiveness to different intensities of light 
is shared by other plants, such as Oxalis, Phaseolus, Trifolium, 
Vida, etc. 
Mimosa pudica (modest). Stem herbaceous, beset 
with prickles, 1 foot high. Leaf-stalks bristly; leaves 
divided into two (sometimes three) pairs of pinnae, each with many 
leaflets (ten to fifteen or more pairs). Flowers small, red, in compact 
heads; June and July. 
M. sensitiva (sensitive). Stems twining, prickly, 3 to 6 feet high. 
Leaflets egg-shaped, hairy beneath, smooth above; there are but two 
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