DIV. n ANGIOSPERMAE 609 



the result of lateral branching during the development of the leaf. 

 The margin of the leaf presents considerable variety. The venation 

 is as a rule reticulate (Fig. 601). 



The flowers in Dicotyledons are typically pentamerous and penta- 

 cyclic, but there are numerous exceptions to this. The floral formula 

 in the most regularly constructed representatives is K5, C5, A5 + 5, 

 G5. 



Series I. Choripetalae 



A. MONOCHLAMYDEAE 



The following orders 1-4 agree in the unisexuality and anemo- 

 phily of their flowers with simple uncoloured perianth. They include 

 various transitional forms from chalazogamy to porogamy. 



Order l. Juglandiflorae 



Family Juglandaceae. Conspicuous, monoecious trees of the northern hemi- 

 sphere with impari pinnate, aromatic leaves arranged alternately. Stipules wanting. 



The Walnut, Juglans regia (Fig. 602), is the best-known representative of the 

 family. It is endemic in Western Asia and the eastern portion of the Mediter- 

 ranean region, but the tree is in cultivation throughout Europe. In spring the 

 axillary buds of the previous season produce long, thick, pendulous catkins bearing 

 numerous flowers. Each of the latter has 3-5 perianth segments, and these together 

 with the two bracteoles are adherent to the bract and surround the numerous 

 stamens, which face towards the tip of the inflorescence. The female flowers in 

 smaller numbers are borne at the summit of the young shoots. The two carpels 

 terminate in large, feathery, diverging stigmas. The perigone is adherent to the 

 bract and bracteoles and reaches to the summit of the inferior ovary. The single 

 loculus encloses an atropous, basal ovule. Fruit, a drupe. The exocarp contains 

 abundant tannin. The hard endocarp is divided into two valves in the plane 

 of the dorsal sutures of the coherent carpels, the limits of which are indicated 

 by the partial septum at the lower part of the fruit. Within the stone is the 

 embryo, enclosed in a thin seed-coat. The large cotyledons, which contain oil, 

 are lobed in correspondence with the false septa that project from the inner surface 

 of the ovary. Endosperm wanting. Other species of Juglans and Carya yield 

 edible seeds and valuable timbers. 



Order 2. Quereiflorae ( 18 ) 



Trees or shrubs usually with entire leaves and deciduous stipules. 

 Monoecious. Flowers in catkins. Ovary inferior ; ovules pendulous. 

 Fruit, a one-seeded nut. Endosperm wanting. Anemophilous. This 

 order includes most of our important forest-trees. 



Family 1. Betulaceae. Male flowers adherent to the bracts. Ovary bilocular, 

 with two long stigmas ; a single, pendulous ovule in each loculus. Mainly 

 distributed in the northern hemisphere. 



2R 



