SE^"SITIYE PLANTS. 
33 
state the result of his experiments relating to the difference 
between the two classes of phenomena above mentioned. After 
describing, with greater accuracy and detail than any previous 
writer, the diurnal and nocturnal movements that occur in the 
leaves and leaflets of the Mimosa pudica, and showing that they 
do not differ, in appearance, from those which ensue as a conse- 
quence of external stimulus, except that in the latter case the 
action is sudden not gradual, M. Bert proceeds to say that the 
causes of the phenomena are not the same in both instances. 
Ether arrests and prevents the movements brought about under 
ordinary circumstances by external stimuli, while the diurnal and 
nocturnal raising and lowering of the leaves are not affected by 
that agent. The last named actions may be induced artificially 
by removing the upper portion of the petiolar “coussinet,” and 
then placing on the cut surface a drop of water ; this is rapidly 
absorbed by the cellular tissue of the lower portion of the swell- 
ing, and the leaf-stalk becomes raised or pressed upwards in 
consequence. On the other hand, if a drop of glycerin be 
placed on the wound, the reverse action takes place and the 
petiole is lowered. The nocturnal movements are always caused 
by a slow gradual increase of force in the upper portion of the 
coussinet, accompanied at first by a diminished, subsequently by 
augmented, energy in the lower portion. The mobility that 
follows on excitation, on the other hand, is exclusively due to a 
sudden loss of energy in the lower portion of the petiolar swell- 
ing, though how this is effected remains still a mystery. 
EXPLANATION OF PLATE. 
Fig. 
1. 
2. 
3*. 
4. 
V 
5. 
6. 
7. 
8 . 
V 
9. 
)) 
10. 
11. 
}) 
12. 
Leaf of 'Mimosa pudica, common Sensitive plant, expanded. 
Leaf of the same collapsed. 
Leaf of Oxalis sensitiva, expanded. 
Leaf of Oxalis acetosella, Wood-sorrel, expanded. 
Leaf of the same collapsed during sleep.” 
Transverse section of the “ coussinet,” or pulvinus of Oxalis aceto- 
sella (after Sachs). 
Leaf of Desmodium gyrans, Telegraph plant: a, the terminal 
leaflet ; h, one of the lateral leaflets, which exhibits different 
movements from those exercised by a. 
Leaf of Bioncea muscipula, Ely-trap ; the leaf-stalk is here dilated 
and flat, and supports a roundish blade, fringed with stiff hairs. 
Leaf of Fly-trap ; the blade shown as folded in halves. 
Stamens of Parnassia, showing how they bend inwards towards 
the pistil. 
Stamens of Parietaria at first coiled up within the flower, but 
liberating themselves with an elastic movement when the pollen 
is ripe. 
Stamen of Berheris, showing the flap of the anther which springs 
up to liberate the pollen. 
VOL. VII. — NO. XXVI. D 
