The family which is most highly advanced is that of the flowering plants, but the others, too, are well worth study, and we will now notice some of the points about their structure which are characteristic of each of the families. CHAPTER XXIII. FLOWERING PLANTS =All the plants which have flowers are put into one big family=, about which you already know a good deal, because nearly all the plants we have studied up to the present have been plants which have flowers. Let us now go systematically over the chief points about their structure, so that we may have a clear idea of their characters, and be able to compare other families with them. 1. We find that ~the plant body is clearly marked out into root, stem, leaves, and flowers~. The stem may be green and delicate, or it may be thick and strong like an oak tree, and on the stem or its branches we find the leaves. 2. The stem and root have definite strands of “water-pipe” cells, and very often the stems have many rings of wood, one of which is added every year. 3. The leaves are very various in the different plants, but they are generally thin and big, though they are seldom much more compound than those of the sensitive plant. 4. The flowers are easily recognized, as a rule, and consist of a number of parts, some of which are often brilliantly coloured. The stamens and carpels are generally in the same flower. 5. ~The seeds are always enclosed within the carpels~, and have generally two seed-coats. 6. Within the seed ~are always either two cotyledons~, as in the bean, ~or one cotyledon~, as in the grasses. Thus when the seedling grows out of the seed it may have two first leaves or one only. These are the chief characters of the whole big family of the flowering plants, but this big family is separated into two smaller groups ~according to the number of cotyledons in the seed~. Those that have two form the group of ~Di~cotyledons, those with one the group of ~Mono~cotyledons. This may not seem a very important point to form the ground for separating plants with flowers so alike as tulips and roses, but we find that, as well as the number of cotyledons, many other differences distinguish the two groups when we separate them in this way. For example, the ~Dicotyledons have the veins of their leaves so arranged as to form a network~, as in the lime, while the ~Monocotyledons have them parallel~, as we noticed in the grasses and lilies. We also find that it is ~only in the Dicotyledons~ that the plants have ~rings of wood in their stems~, as is the case in the lime, oak, and many others. In the numbers of the parts of the flower, we also find differences between the two groups; for example, the ~Dicotyledons~ have generally two, four or five, or a multiple of these numbers such as ten, as we see in the poppy, primrose, rose, and many others; while the ~Monocotyledons~ have the parts of their flowers in three or multiples of three, as in the lily, tulip, and daffodil.