270 HISTORICAL PALAEONTOLOGY. 



cotyledons.* In Europe the plant-remains in question have 

 been found chiefly in certain sands in the neighborhood of Aix- 

 la-Chapelle, and they consist of numerous Ferns, Conifers (such 

 as Cycadopteris), Screw Pines (Pandanus), Oaks (Quercus), 

 Walnut (Juglans), Fig. (Ficus), and many Proteacea, some of 

 which are referred to existing genera (Dryandra, Banksia, 

 Grevillea, &c.) 



In North America, the Cretaceous strata of New Jersey, 

 Alabama, Nebraska, Kansas, &c., have yielded the remains of 

 numerous plants, many of which belong to existing genera. 

 Amongst these may be mentioned Tulip-trees (Liriodendron) , 

 Sassafras (fig. 186), Oaks (Quercus), Beeches (Fagus), Plane- 

 trees (Platanus), Alders (Alnus}, Dog-wood (Cornus), Willows 

 (Salix), Poplars (Populus), Cypresses (Cupressus}, Bald Cy- 

 presses (Taxodium), Magnolias, &c. Besides these, however, 

 there occur other forms which have now entirely disappeared 

 from North America as, for example, species of Cinnamomum 

 and Araucaria. 



It follows from the above, that the Lower and Upper Creta- 

 ceous rocks are, from a botanical point of view, sharply sepa- 

 rated from one another. The Palaeozoic period, as we have 

 seen, is characterized by the prevalence of " Flowerless " plants 

 {Cryptogams), its higher vegetation consisting almost exclu- 

 sively of Conifers. The Mesozoic period, as a whole, is charac- 

 terized by the prevalence of the Cryptogamic group of the 

 Ferns, and the Gymnospermic groups of the Conifers and the 

 Cycads. Up to the close of the Lower Cretaceous, no Angio- 

 spermous Exogens are certainly known to have existed, and 

 Monocotyledonous plants or Endogens are very poorly repre- 

 sented. With the Upper Cretaceous, however, a new era of 

 plant-life, of which our present is but the culmination, com- 

 menced, with a great and apparently sudden development of new 

 forms. In place of the Ferns, Cycads, and Conifers of the earlier 



* The " Flowering plants " are divided into the two great groups of 

 the Endogens and Exogens. The Endogens (such as Grasses, Palms, Lilies, 

 &c.) have no true bark, nor rings of growth, and the stem is said to be 

 " endogenous ;" the young plant also possesses but a single seed-leaf or 

 " cotyledon." Hence these plants are often simply called " Monocotyledons." 

 The Exogens, on the other hand, have a true bark ; and the stem increases 

 by annual additions to the outside, so that rings of growth are produced. 

 The young plant has two seed-leaves or " cotyledons," and these plants 

 are therefore called " Dicotyledons." Amongst the Exogens, the Pines 

 {Conifers) and the Cycads have seeds which are unprotected by a seed- 

 vessel^ and they are therefore called "Gymnosperms." All the other Exo- 

 gens, including the ordinary trees, shrubs, and flowering plants, have the 

 seeds enclosed in a seed-vessel, and are therefore called " Angiosperms." 

 The derivation of these terms will be found in the Glossary at the end of 

 the volume. 



