32 THE TRUE GRASSES. 



pear iu varieties that may even be regarded as corre- 

 sponding species. Not less than 90 genera are common 

 to both continents ; among these are many that are ex- 

 clusively tropical, and besides ten are single types. No 

 one tribe is confined to one hemisphere, and no genus 

 of numerous species to any one floral region. All this 

 goes to prove that grasses are a family distributed very 

 uniformly, and that the separation of their tribes goes 

 back to very ancient times. To be sure, the single tribes 

 have varied under the influence of the later divisions into 

 zones ; while the Panicew and Andropogonece preponder- 

 ate in the tropics, they are put in the background by the 

 Festucece., Avenece, and Hordece in the temperate and frigid 

 zones. The eastern North American forest region has 

 preserved many more of them (and in general of tropic- 

 types) than has the Old World. 



Fossil Grasses. — It cannot be doubted that during the 

 past geological ages, and especially in the tertiary period, 

 grasses must have been widespread and abundantly de- 

 veloped. The numerous remains of grass-like leaves are 

 a proof of this, but any botanist who has made the matter 

 a study will regard as a complete failure the efforts of 

 some phyto -palaeontologists to fix upon relations to liv- 

 ing species from the crushed and compressed spikes and 

 sjDikelets. The fragments described as Poacites Brongn., 

 Arundinites Sap., Psemlophragmites Sap., Pcdeopyrum 

 Schmalh., may be entirely passed over; but even others, 

 whose forms point towards the living genera Oryza, Pani- 

 curn, Uniola, and consequently may lead to conclusions as 

 to the reasons of the existing geographical distribution, 

 are not sufficiently characterized for the determination of 

 genera. There are still others which with good reasons 

 may be referred to Arundo, Phragrnites, and perhaps to 

 the Bambusece. (Engler.) 



Relations. — The grasses form a very isolated family, 

 showing close relationship only to the Cyperacea?, but 

 markedly differing in the structure of the fruit and em- 

 bryo (outside position, shield-shaped cotyledon, etc.). 

 The number of species is uncertain, since our knowledge 

 of them is made obscure by a mass of synonyms. There 



