66 THE HUMAN SIDE OF PLANTS 
abundantly; and a striking thing in its appearance 
is the reddish-pink colour of its stems. 
Other “petty thieves” are the Castilleja, or 
painted-cup, Gerardias, and numerous other small 
plants. 
It is generally known that plants which are whol- 
ly parasitic in habit have, with a few exceptions, 
lost their green colouring-matter; and many have 
lost their leaves. On the other hand, those which 
are only half parasitic in habit still have the colour- 
ing-matter in their leaves, but, like the mistletoe, 
the leaves have a pale greenish tinge, suggestive of 
degeneration into yellow. 
Plants are likely to become robbers and murder- 
ers only when driven to it by unavoidable condi- 
tions, such as are found in the great forests and 
in the tropical jungles, where the trees and plants 
are so closely tangled that their heads intermingle, 
forming an almost impenetrable canopy above and 
refusing sunlight to the ground plants and less 
altitudinous trees. These minor plants are forced, 
in order to live, to fight their way, by fair means 
or foul, up to the sunlight: unless they do so, they 
must weaken and die in the gloomy undergrowth 
below. It is the eternal struggle, the fight to 
exist, with the lower plants either dying out or de- 
generating under the oppression of the higher 
