Plant life, then, seems to be better provided with means to renew itself than most animals, for, as we have seen, it has several methods to rely on. These may be divided into sexual, which includes both that in flowering plants with their visible mating and in flowerless plants with invisible mating, and _asexual_, literally without sex. In the latter are all those unicellular plants that reproduce themselves by simple division of the cell, and also those flowering plants that either naturally, as in life plant, or by the gardener’s art of making cuttings, produce new plants quite without the intervention of the sexes. Whether it be sexual or asexual, nature has more than fulfilled its obligation to the plant world in providing it opportunities for self-renewal. No matter what apparently unfavorable condition arises and often in spite of an almost unbelievable wastage of potential life stuff, the renewal goes on, or else there is the total disappearance of the species. So strong is this tendency to provide for renewal of their kind that many plants, if injured or cut by a mower, will almost in their last gasp hurriedly flower and set seeds, and we have already seen that the little liverwort, even if cut to pieces, also obeys that nearly universal law of nature: “Be fruitful and multiply.” CHAPTER IV THE FAMILIES OF FLOWERING PLANTS AND THEIR RELATIONSHIP There are perhaps over 150,000 different kinds of flowering plants known in the world to-day, but the flowerless ones are fewer than these in numbers. No one really knows how many thousands of the cryptogams there may be in the world, for all of them have not yet been described, and there are doubtless thousands of which we merely suspect the existence. Flowering plants are so much better known, and have for 2,000 years been the subject of scientific writings, that their relationships and obvious groupings into families are fairly definite and often easily recognizable. In our ordinary discussions or gossip of neighbors or relatives, the absolutely necessary starting point is to know their name. Their acquirement of this by christening, or by the adoption of it through the usage of parents, settles for life what they will be called. Plants are also christened, and that ceremony is one of the most important events in our subsequent discussion of them. PLANT NAMES AND HOW THEY ARE ACQUIRED As we always have at least two names, one to show that we are a Smith, for instance, and another to fix us as John Smith, so all plants have two names, sometimes three.