Commencing at the bottom of the scale, we find the Thallogens, or flowerless plants which lack proper stems and leaves,--a class which includes all the algæ. Next succeed the Acrogens, or flowerless plants that possess both stems and leaves,--such as the ferns and their allies. Next, omitting an inconspicuous class, represented by but a few parasitical plants incapable of preservation as fossils, come the Endogens,--monocotyledonous flowering plants, that include the palms, the liliaceæ, and several other families, all characterized by the parallel venation of their leaves. Next, omitting another inconspicuous tribe, there follows a very important class,--the Gymnogens,--polycotyledonous trees, represented by the conifers; and cycadaceæ. And, last of all, come the Dicotyledonous Exogens,--a class to which all our fruit, and what are known as our "forest trees," belong, with a vastly preponderating majority of the herbs and flowers that impart fertility and beauty to our gardens and meadows. This last class, though but one, now occupies much greater space in the vegetable kingdom than all the others united. Such is the arrangement of Lindley, or rather an arrangement the slow growth of ages, to which this distinguished botanist has given the last finishing touches. And let us now mark how closely it resembles the geologic arrangement as developed in the successive stages of the earth's history. [Illustration: Fig. 1.[4] -+------------------------- | Thallogens. Silurian. | | Acrogens. -+-----+------------------- | | | Gymnogens. Old Red. | | | | | | -+-----+-----+------------- | | | | Monocotyledons. Carboniferous. | | | | | | | | -+-----+-----+-----+------- Permian. | | | | -+-----+-----+-----+------- Triassic. | | | | -+-----+-----+-----+------- | | | | : Dicotyledons. Oolitic. | | | | : | | | | | -+-----+-----+-----+-----+- | | | | | Cretaceous. | | | | | | | | | | -+-----+-----+-----+-----+- Dicotyledonous Trees. | | | | | Tertiary. | | | | | | | | | | -+-----+-----+-----+-----+- Geologic [Thal. Ac. Gy. Mon. Dic.] arrangement. Lindley's [Thal. Ac. Mon. Gy. Dic.] arrangement. THE GENEALOGY OF PLANTS.]