In the life plant--a thick-leaved shrub from Mexico commonly grown in greenhouses--the leaves are wavy margined. From their edges, especially when injured, many tiny new plants will often start to grow. Even if the leaf is cut up into fairly small pieces many of these will develop young plants, and in various forms of the common rex begonia the leaves are usually cut into small pieces by gardeners for the production of young plants which always sprout from such pieces. It is useless to multiply such cases, as everyone knows of the production of young plants from the ends of strawberry runners, the cutting up of potatoes, the universal garden practice of making cuttings, and the sprouting of willows, all of which are effective by virtue of this faculty of plants to produce young quite without the intervention of different sexes. Not so well known are the cases of a liverwort, a small relative of the mosses, which, if chopped into fine pieces, each will develop into a new plant. We have already spoken of the spawn of mushrooms; and even on sphagnum moss, in addition to its sexual reproduction, it produces sterile branches that will root and, after separation from the old plant, form a new one. Wherever this tendency is found, whether it be in a microscopic seaweed, some of which know no other means of reproduction, or in the showy begonia, it depends for its success upon a property of the ultimate unit of its structure, the cell. Sometimes, as in bacteria or the most minute seaweeds and in some other kinds, the whole plant consists of a single microscopic cell, when it is said to be a _unicellular_ plant. All others, in which the grouping or modifications of the cell makes more complex structures, such as trees or shrubs and all the plants that grow, both flowering and flowerless, are called _multicellular_ plants. Whether they be of one or many cells, these have the faculty of dividing, and by this division making two where one existed before the division. This division of cells is what happens in the normal growth of plants and it is this division, in more unusual ways, that results in the production of new plants without mating of the sexes. As cells are themselves microscopic, of course their division is equally so, and cannot be described in detail here. It has been many times described and pictured both in books on plants and animals, as it is the ultimate unit of the structure of both.