i8o4 A TEXTBOOK OF THEORETICAL BOTANY 



species which are commonly cukivated, it is also of considerable economic 

 importance not only for its timber but also because of the Maple Sugar 



which it yields. 



Acer campestris is the Field Maple, a common British plant which forms 

 a large shrub or small tree. The flowers (Fig. 1698) are produced in racemes; 

 they are pentamerous with eight stamens developed in two whorls, while the 



Fig. 1698. — Acer pseiidoplatamis. In- 

 florescence. 



ovary is composed of two carpels with two collateral or superimposed ovules 

 in each loculus. The fruit is a schizocarp composed of two one-seeded 



samaras. 



Acer pseudo-platanus, the Sycamore, is a large forest tree common 

 in Britain though not a native. The inflorescence is a raceme. The leaves 

 are palmate and are frequently attacked by the fungus Rhytisma acerinum 

 which causes large black spots resembling tar. 



Acer saccharinum, the Sugar Maple, grows in the eastern United 

 States and Canada. It yields from 2 to 4 lb. of maple sugar a year. This 

 sugar is obtained mainly in the early spring by boring holes in the trunk, 

 and collecting and evaporating the liquid exuded from the xylem. 



Acer fiegundo, another species closely resembling the Sycamore, is 

 commonly cultivated in this country. It is dioecious, the male inflorescence 

 being an umbel while the female inflorescence is raceme. Pollination is by 

 long- or short-tongued insects which collect the nectar which is exuded 

 copiously. The lateral buds, as in the Plane, are protected by the base of the 

 petiole. Many small and beautiful species of Acer are cultivated in Japan. 

 Some of these are quite small bushes, with finely dissected leaves which 



