No two plants or parts of plants are identically exposed to the conditions in which they live. The large branches in Fig. 1 probably had more room and a better exposure to light than the smaller ones. Probably no two of the leaves in Fig. 2 are equally exposed to light, or enjoy identical advantages in relation to the food that they receive from the tree. Examine any tree to determine under what advantages or disadvantages any of the limbs may live. Examine similarly the different plants in a garden row (Fig. 3); or the different bushes in a thicket; or the different trees in a wood. The plant meets its conditions by _succumbing to them_ (that is, by dying), or by _adapting itself to them_. The tree _meets the cold_ by ceasing its active growth, hardening its tissues, dropping its leaves. Many herbaceous or soft-stemmed plants meet the cold by dying to the ground and withdrawing all life into the root parts. Some plants meet the cold by dying outright and providing abundance of seeds to perpetuate the kind next season. [Illustration: FIG. 4.--THE REACH FOR LIGHT OF A TREE ON THE EDGE OF A WOOD.] Plants _adapt themselves to light_ by growing toward it (Fig. 4); or by hanging their leaves in such position that they catch the light; or, in less sunny places, by expanding their leaf surface, or by greatly lengthening their stems so as to overtop their fellows, as do trees and vines. The adaptations of plants will afford a fertile field of study as we proceed. =Struggle for existence= and =adaptation to conditions= are among the most significant facts in nature. The sum of all the conditions in which a plant or an animal is placed is called its =environment=, that is, its surroundings. The environment comprises the conditions of climate, soil, moisture, exposure to light, relation to food supply, contention with other plants or animals. _The organism adapts itself to its environment, or else it weakens or dies._ Every weak branch or plant has undergone some hardship that it was not wholly able to withstand.