It might almost seem as if demoralization, so far as food habits are concerned, had reached its lowest point in these plants that literally rob the dead, but there are still lower depths to which certain plants have been reduced. This consists of robbing the living, and such plants are called _parasites_, a word perfectly familiar in other connections. Parasitic plants have no roots, but attach themselves to the roots of other plants, somewhat generously called _hosts_, from which they derive their food. The best known case is the common Christmas mistletoe, and the dodder (Figure 68), but there are hundreds of others. Nothing in all the realm of plant life so perfectly fits the action to the word as plants of this type, flourishing when the host flourishes, dying when it dies. Producing flowers and seeds, and often, by an irony of fate, perfectly green leaves, they are nevertheless the most debased of all plants in their mode of life. These successive steps in the degradation of food habits, are not always the clean-cut things they might be inferred to be from the foregoing. There are many intermediate stages; it may even prove to be the case that some plants are wholly autophytic at certain stages of their life, and slip partially into more devious practices at other stages. The whole affair is not yet thoroughly understood and may well be the result of competition, as it is quite conceivable that if the getting of food in normal ways became difficult or impossible plants may have had to resort to other methods. [Illustration: FIG. 68.--THE DODDER A leafless parasitic vine which steals its food from the plants to which it is attached.] 4. WHAT PLANTS DO WITH WATER AND HOW THEY BREATHE Some one has said that one day without water would make men liars, in two days they become thieves, and after the third or fourth day they would kill to get water. In the Army Records at Washington is a report of one of our expeditions, which in chasing Indians got lost in a desert, and in which the soldiers fought among themselves for even the most repulsive liquids. It hardly needs these gruesome examples, however, to confirm what everyone who has ever been mildly thirsty knows, that water is an essential for all animals, and that to be without it is to suffer torture. Air of the proper kind is just as important, and because its absence or impurity causes more sudden agony and a quicker death, the need of it is that much more acute. Plants rely even more upon these two essentials of life, and in getting them they behave in ways just as ruthless as do men who are suddenly deprived of either of them.