Page:An introduction to physiological and systematical botany (1st edition).djvu/169

 Rh ''Pyrus Malus, Engl. Bot. t.'' 179; and I cannot but assent to Mr. Knight's opinion, that each individual thus propagated has only a determinate existence, in some cases longer, in others shorter; from which cause many valuable varieties of apples and pears, known in former times, are now worn out, and others are dwindling away before our eyes. New varieties of Cape Geraniums, raised from seed in our greenhouses, are of still shorter duration, and can be preserved by cuttings for a few successive seasons only; yet several of these stand in our botanic works, with all the importance of real species. Gardeners know how many of the most hardy perennial herbs require to be frequently renewed from seed to exist in full vigour; and though others appear to our confined experience, unlimited in that respect, we have many reasons to believe they are not so. Propagation by seeds is therefore the only true reproduction of plants, by which each species remains distinct, and all variations are effaced; for though new varieties may arise among a great number of seedling plants, it does not appear that such varieties owe their