518 



PART IV. CLASSIFICATION. 



are acuminate and gray on the under surface ; in A. glutinosa, the black or 

 common Alder, they are obovate or even emarginate, and green on both 

 surfaces. In Alnus viridis, the Mountain Alder, only the $ catkins 

 are destitute of bud-scales in the winter : the fruit is winged, 



Betula, the Birch. In both kinds of catkins the three flowers have only 

 the bracteoles a and /3. In the $ flowers the perianth is usually incom- 

 plete, and there are only two stamens, the filaments of which are forked. 

 In the ? catkins, the two bracteoles cohere with the bract to form a three- 

 lobed scale which falls off together with the winged fruit. The $ cat- 

 kins are borne terminally on the shoots of the previous year, and are not 

 covered with bud-scales during the winter ; the $ catkins are borne ter- 

 minally on lateral dwarf-shoots which have only a few leaves, and they 

 are enclosed by bud-scales during the winter ; as a consequence, flowering 

 takes place after the unfolding of the leaves. The shoots of successive 

 years form sympodia, and the leaves are arranged spirally. B. verrucosa has 

 white glands on the leaves and young shoots : B. pubescens has no glands, 

 but the shoots are hairy ; it is a northern form : B. fruticosa and 

 B. natia are shrubs occurring in high latitudes : B. alba is the common 

 Birch. 



FIG. 328. A Scale from a (J catkin of 

 Alnus incana : the axillary branch adheres 

 to the scale (s), it bears four bracteoles and 

 three flowers: two of the flowers are seen 

 laterally (I/ b'), the median one from above ; 

 p perianth ; a stamens. B Bract (s) of a $ 

 catkin of the same plant : its axillary branch 

 bears two lateral branches, each of which 

 bears two bracteoles (v v) and one flower ; / 

 the ovary ; n the stigmata (magnified and 

 diagrammatic). 



Flo. 329. Alnus glutinosa. A Branch 

 bearing catkins (in winter). B a group of 

 <J flowers (from above). C The same after 

 removal of flowers (lateral view). E Group 

 of ? flowers, seen from within. F The 

 same after the removal of the flowers, ff 

 a scale from the ? catkin : 6 bract ; o, /3, j3' 

 bracteoles. 



Order 2. CORYLACE^E. Flowers monoecious, in $ and ? cat- 

 kins. The <$ flowers have no perianth ; that of the $ flower is 

 rudimentary. The inferior ovary is bilocular ; one loculus is 

 sterile, the other contains two suspended anatropous ovules : the 

 fruit is one-seeded and indehiscent (a nut). Two flowers are borne 

 in the axil of the bract of the ? catkin, the median flower being 

 absent. The one-seeded fruit is surrounded by a leafy investment 

 (cupule) formed by the three bracteoles (a a! ft' and /fa' ft' 



