Seeds have inside them a tiny plantlet folded and ready to grow when the seed splits to release it. Also, in the seed is stored up food to sustain the new plant until such time as its own roots begin to act. This young plantlet is known as the _embryo_, and to this all actions of the seed are subservient. As the seed splits, and the young plant develops its first leaves and rootlets, there is shown one of the most remarkably uniform tendencies in plant life. In all plants with net-veined leaves the young plantlet starts life with two leaves, or _cotyledons_, as these first leaves are called, and this whole group of plants are thus known as _dicotyledons_. In plants with parallel-veined leaves the young plantlets start out with a single cotyledon and are therefore called _monocotyledons_. In only the pines, spruce, and a few other evergreen trees the seedling plants have several cotyledons and are known as _polycotyledons_. All the flowering plants in the world belong to one of these groups, so that merely to see the germinating seed tells the story at once. The linking of parallel-veined leaves and a single seed leaf, and net-veined leaves with two seed leaves, is also associated with very definite arrangement of their flower parts, their method of growth and other characters. Something has already been said of this in the discussion of stems and leaves, and more will be found in the chapter on plant families. No more beautiful example of the plan or scheme of nature is to be found than these characteristics of all plants, and in seeds we find the first hint as to which army the plant will join, under which banner it will fight, and under what generalship it will develop. Nothing tells us so much as these first seed leaves, pushing their way up through the soil and revealing, as they burst above ground, to what place in nature their destiny will consign them.