78 AN INTRODUCTION TO THE STUDY OF FOSSILS 



sperms, — • the true flowering vegetation, — was probably due to 

 the pari passu development of flower-loving insects, the bees and 

 wasps (Hymenoptera) and the butterflies and moths (Lepidop- 

 tera) ; these families first appeared in the Jurassic, the period 

 immediately preceding the one which apparently saw the begin- 

 ning of the angiosperms. 



Derivation of name. — Angiospermae > Greek angeion, a 

 vessel + sperma, seed, because the seed is inclosed in a pro- 

 tecting ovary, e.g. the core of an apple, the pit of a cherry, the 

 chaff of grass. In the gymnosperms the pollen can reach the 

 ovules directly. 



The Angiospermae are divided into the classes : — 



a. Monocotyledones. 



b. Dicotyledones. 



Class i, ^Ionocotyledones 



These plants are usually distinguished by the following char- 

 acters : the plant begins with a single leaflet or cotyledon 

 (whence the name mono-cotyledon) ; the leaves are parallel- 

 veined ; the stem is cylindrical with the vascular bundles scat- 

 tered, a cross section accordingly not showing concentric growth 

 lines ; the roots are fibrous ; the parts of the flowers in threes. 



This class includes to-day members of vast economic impor- 

 tance to man. The grasses, especially their fruit, the grains, 

 have become an absolute necessity to him in the temperate 

 zones, just as the plantain, banana, and various palms (e.g. 

 date, coco and sago palms) are now an essential to his existence 

 within the tropics. Representatives of the class are first known 

 from the Upper Comanchean of eastern North America and 

 Portugal in such lowly forms as the pondweed and sedge ; the 

 lily and palm, however, soon appeared in the Cretaceous, while 

 not until rather late in the Tertiary did true grasses make their 

 appearance. 



The paleontologic record of the palms goes back to the mid- 

 Cretaceous (Fig. 28). It is probable that they occurred 



