MOVEMENTS OF GROWING LEAVES AND FLORAL ORGANS. 87 1 
tropism is shown by the fact that the revolving nutation takes place more quickly 
towards the light than away from it. Some tendrils, strikingly those of the Virginian 
Creeper and Bignonia capreolata, have the remarkable power of developing broad discs 
at the end of their branches when they remain in contact for some time with hard 
bodies, which attach themselves like cupping glasses to rough surfaces, and enable the 
plant to climb up vertical walls when it finds no slender support round which it can coil. 
In this case it is obviously necessary that the tendril should turn towards the wall which 
serves as its support in order to become attached to it, and this is effected by negative 
heliotropism, which causes the tendril to approach the wall shaded by foliage, where it 
now performs its revolving movements of nutation — one might almost say its groping 
movements — creeps along the surface, finds out the crevices and depressions, and 
developes its adhesive discs. 
Sect. 26. — Movements of growing Leaves and Floral Organs produced 
by variations of Light and of Temperature ^ In the foregoing paragraphs we 
have become acquainted with the movements of curvature of growing organs v^^hich 
take place when the external conditions are constant, movements which are pro- 
duced by the more rapid growth of the one or of the other side of the organ under 
the action of purely internal causes. These movements were termed ' spontaneous 
nutations.' Amongst the organs endowed with spontaneous nutation we found that 
tendrils are pecuhar in being sensitive to contact on one side and in that the slight 
pressure of the support induces a more rapid growth of the free surface, and a much 
less rapid growth of the surface with which it is in contact. Many growing foliage- 
leaves and floral organs, possessing, like tendrils, a bilateral organisation, are stimu- 
lated to curve by variations of temperature or of the intensity of light, the growth of 
one side or the other being either accelerated or retarded. 
It is not all growing leaves and flowers that are sensitive to these meteorological 
influences ; among plants which are very closely alHed some do and some do not 
possess this property. Pfeffer mentions, as examples of sensitive growing leaves, in 
addition to the very sensitive leaves of Impatiens nolitangere, those of Chenopodiese, 
Atripliceae, Solanese, Mimulus ti'grinus, Mirabilis Jalapa, of species of Sikne and 
Ahine, and of many Compositse ; to this list Batalin adds Malva rotundifolia, (Eno- 
thera sp., Portulacca oleracea, Linum grandtßorum, Stellaria media, Gnaphalium uh'gi- 
nosum, various species of Polygonum, Senecio vulgaris, Sida NapcBa, Rumeax Hydrola- 
palhum, IpomcBa purpurea, and Brassica oleracea, and doubtless further investigation 
will increase the number. The movements of these leaves are not effected by means 
of special organs, but it is the petiole or the lower part of the lamina of the leaf 
which curves, under the meteoric influences, upwards or downwards accordingly as 
the growth in length of the upper or of the low^er surface has been accelerated by 
them. The mode of antagonism of the two sides of the bilateral organ is different 
in different species : in some the leaves are raised at night, as in Chenopodium, 
Brassica, Polygonum aviculare, Stellaria, Linum, in others the leaves fall, as in 
* Pfeffer, Physiologische Untersuchungen, Leipzig 1873, and Sitzungsber. der Ges. zur Beförd. 
der ges. Naturwiss. zu Marburg, 1873. — Batalin, Flora, 1873. 
[Pfeffer, Die Periodischen Bewegungen der Blattorgane, 1875. — Darwin, Movements of Plants. 
— Wiesner, Die heliotropische Erscheinungen, II.] 
In these works full references are given to the older literature of the subject. 
