SENSITIYE PLANTS. 
27 
One more illustration — perhaps the most extraordinary of all 
— is afforded by the Telegraph plants Desmodium gyrans, 
a native of India. The leaves of this plant consist of three 
leaflets — two small lateral ones, and a third, much larger, 
terminal one. If the Desmodium be watched, the terminal leaflet 
may be observed to move upwards or downwards, according to 
the intensity of the light ; the lateral leaflets having a still more 
vigorous and perfectly independent action, recalling that of the 
old Semaphore signals, and one which is going on day and 
night alike, and hence is unaffected by the light. The action of 
these smaller leaflets is so singular as to demand a more exact 
description than is called for in the other instances. Supposing 
one of the smaller leaflets to be in the horizontal plane, if 
watched it may be seen to rise by a succession of little jerks, 
keeping its point and upper surface directed towards the stem. 
When it has attained a nearly vertical direction its companion 
leaflet begins to descend, turning its upper surface away from 
the stem as it falls. Having descended to the horizontal posi- 
tion, the other leaflet begins to rise again, and so on. Electrical 
and mechanical stimuli appear to have no effect on these move- 
ments, though heat and moisture accelerate them. They are 
perfectly perceptible in our stoves, but less so than under 
natural circumstances. These motions are, perhaps, the most 
mysterious of any, and, though much has been written con- 
cerning them, we know little more than when they were first 
brought under the notice of the scientific world b}^ Lady Monson, 
in the latter part of the last century. 
The phenomena that take place in the flower are not less 
worthy of observation than those of the stem and leaves. The 
folding and unfolding of the flowers, sometimes at regular hours, 
did not escape the observant Linnaeus, since whose time, indeed, 
but little addition has been made to our knowledge of this branch 
of the subject ; but it is one that sadly requires fuller investiga- 
tion. How is it, for instance, that the Sidas of India expand their 
flowers in the morning only, while the Abutilons, which scarcely 
differ from them in any point of structure, yet unfold their 
blossoms in the evening only. The movements that take place in 
the stamens and pistils have, however, attracted more general 
attention, because in many cases the mobility is excited by 
mechanical stimulus ; a slight touch with a pin or the antenna of 
an insect will suffice to cause the stamen of Berberis to bend 
suddenly inwards towards the stigma, there to deposit its pollen. 
But the mere enumeration even of the many instances of mo- 
bility in connection with the dispersal of pollen or of the seed 
would occupy more space than we can give to the subject, and 
so we pass on to the anatomy of the mobile organs. We cannot, 
of course, give the details in every case where motion has been 
observed, but we may state in general terms that it has been 
