[Illustration: Fig. 104. Sensitive tendrils of the Pea. (~t~) tendril at the end of foliage leaf, (~o~) ordinary leaflets.]
In vines and marrows we also get tendrils, but they are not modified leaves, but special branches which have become sensitive.
In some plants the sensitive tendrils do not twine, but instead form little sticky suction pads at their tips whenever they come in contact with the support, and these hold the tendril very firmly on, as you can see in the ampelopsis, which grows right up the walls of houses. If you look under the thick covering of leaves, you will find these tiny padded tendrils clinging tightly to the wall (~see~ fig. 105). This is the reason that the ampelopsis grows so well up the walls without being held up artificially.
There are many other things you may find out about climbing plants, but you will have seen enough to be able to look for more for yourself, and to understand how it is that the climbing plants can reach such a great height so quickly. ~They have learnt to avoid the trouble and expense of building strong supporting stems for themselves, and by getting their support from others, they are able to grow quickly out into the good positions for the light which they could not otherwise have reached.~
[Illustration: Fig. 105. Ampelopsis, which supports itself by the little suction pads developed at the ends of the tendrils.]
We call a plant or animal a ~Parasite~ when it does no food-building for itself, but adapts its whole structure to obtain and use the food made by the work of other plants or animals. Plant parasites generally attach themselves to a “Host” plant so closely that they suck their food from it, and sometimes remain with it till they have finally killed it, and so have destroyed their only source of food and means of life.
Among plants, most of these degenerate creatures belong to the group of ~Fungi~. The rust and smut on wheat, the mildew on fruit, and nearly all the thousand spots, blemishes, and diseases of cultivated and other plants, are the result of the parasitism of some members of the family of fungi. Plants which prey like this on others are without very many of the characteristics of true plants; they become colourless, losing their green substance, and with it all power of building food for themselves, so that they are quite dependent on the host plant, without which they must ultimately die.