The plants found in different strata are either terrestrial or aquatic, and the latter exhibit species allied to the salt and fresh water vegetables of the present day. Their state of preservation depends much on their structure. Cellular plants have probably in a great measure been destroyed, and hence their rarity; while those having a woody structure have been preserved. The following is the number of fossil genera and species, as compiled from Unger's work on Palæophytology--(Unger, Genera et Species Plantarum Fossilium, 1850). DICOTYLEDONES. Genera. Species. Thalamifloræ. 24 84 Calycifloræ 56 182 Corollifloræ 23 60 Monochlamydeæ Angiospermæ 48 221 ------------- Gymnospermæ 56 363 MONOCOTYLEDONES. Petaloideæ 38 130 Glumiferæ 5 12 ACOTYLEDONES. Thallogenæ 31 203 Acrogenæ 121 969 Doubtful 35 197 ---- ---- 437 2421 These plants are arranged in the different strata as follows:-- {Cambrian, Silurian, and Devonian 73 Palæozoic {Carboniferous 683 {Permian 97 {Triassic 115 Mesozoic {Jurassic 294 {Cretaceous 183 {Eocene 414 Cainozoic {Miocene 496 {Pliocene 35 Recent Post-Pliocene 31 ---- Fossil Species. 2421 During the twenty years that have elapsed since this enumeration was made, the number of fossil species has been very greatly increased. The proportion exhibited in this table is likewise greatly altered from the enormous additions made to the Tertiary Flora by Unger, Ettingshausen, and Heer, and from the important contributions by Principal Dawson to the Devonian Flora. Among the fossil Thalamifloral Dicotyledons, Unger mentions species belonging to the orders-- Magnoliaceæ. Anonaceæ. Nymphæaceæ. Capparidaceæ. Malvaceæ. Byttneriaceæ. Tiliaceæ. Aurantiaceæ. Malpighiaceæ. Aceraceæ. Sapindaceæ. Cedrelaceæ. Zygophyllaceæ. Xanthoxylaceæ. Coriariaceæ. Among Calycifloral Dicotyledons-- Celastraceæ. Rhamnaceæ. Anacardiaceæ. Amyridaceæ. Leguminosæ. Rosaceæ. Calycanthaceæ. Combretaceæ. Melastomaceæ. Myrtaceæ. Halorageaceæ. Cucurbitaceæ. Cornaceæ. Loranthaceæ. Rubiaceæ. Among Corollifloral Dicotyledons--