SUMMARY 231 



retain the habit under changed conditions. De Candolle 

 explains early leaf-fall in some cases by introduction 

 from an extreme climate where it would be necessary, 

 and instances the Walnut, introduced from Armenia. 



Another question is, Do the plants which come into 

 leaf early in spring lose their leaves early in autumn, 

 and are the late leafers also tardy as regards defoliation ? 

 Or are the early leafers late to lose their leaves ? The 

 hawthorn hedges are among the first to show signs of 

 green in the spring, and among the last to lose their 

 foliage in the autumn. The Horse Chestnut buds have 

 burst when the Oak and Ash are grey as at midwinter, 

 but the latter retain their leaves the longer. We must 

 remember, too, that the Ash gets its flowering over before 

 leafing, while in the Chestnut the leaf-buds are the first 

 to expand. To try and settle this point De Candolle 

 made a resume of four years' observations in Belgium, in 

 which twenty-eight species or varieties were concerned. 

 He made four lists : A, the early leafers ; B, those with 

 an early leaf-fall ; C, late leafers ; D, those where the 

 fall is late. Each list contains about thirteen names. 

 Two, Spircea sorbifoliaand Lilac, are common to A and B ; 

 that is, out of thirteen early leafers only two lose their 

 leaves early. Four are common to A and D : leaf early 

 but fall late. Two, Walnut and Gleditschia ferox, occur 

 in both B and C, having an early fall, though leafing 

 late; and four are late in leafing and have also a late 

 leaf-fall. It is therefore evident that the time of leaf- 



