Ferns are much like ordinary flowering plants; except for their lack of flowers, they have all the root, stem, and leaf characters of their more showy neighbors. While most of them have compound leaves, even sometimes twice or thrice compounded, a few have simple, narrow leaves without teeth, and one kind in tropical America has threadlike leaves. In many tropical rain forests, so called from their dripping wet condition, ferns form large trees, and these tree ferns are among the most graceful and feathery of all plants. There are, too, a few climbing kinds--one, called the climbing fern, is a native of the eastern United States. Then there is the walking fern, that seems to upset the statement that plants do not move as animals do. It sends out delicate runners that, rooting at the tips, form new plants, often several feet from the parent plant. The characteristic of having, even in the simplest form, stems, leaves, and roots, with all that this implies in their internal structure, marks them off at once from all other flowerless plants. In ferns there is always some internal equipment for carrying food from one part of the plant, the roots, to another, and this ability is possessed by virtue of ducts or vessels through the stem and leaves. This system, found in all flowering plants and ferns, but _nowhere else in the plant world_, is called the _vascular system_, or literally, a vessel system. We shall see how important was the acquirement of this system of vessels, when we get to the chapter on the History of the Plant Kingdom. Its appearance upon the earth marks as important a stage in the development of plants as the dawn of a definite backbone did upon animal life. Ferns, then, are _vascular cryptogams_ because they do have conducting vessels in their stems, and they produce their young by a process of hidden marriage which will be described later. All other cryptogams or flowerless plants are without this system of vessels and are called therefore _non-vascular cryptogams_. Numerically they are tremendously important; upon them depend many manufacturing processes like bread making, brewing, and all arts using fermentation. But they are hardly recognized as plants by the general reader, and because of their size and the necessity of studying them with a microscope in order to understand their structure they will be treated here only briefly. OTHER FLOWERLESS PLANTS