688 NATURAL SCIENCE. ^.^,,, 



originally from somewhat different climates. A plant may have con- 

 tracted the habit through long generations of shedding its leaves 

 early or late, as the case may be, and retain the habit under changed 

 conditions. Thus De CandoUe (17) 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, and 

 the Catalpa and Gleditschia from the eastern United States. 



The question also arises whether plants which come into leaf 

 early in the spring lose their leaves early in the autumn, and whether 

 the late leafers are also tardy as regards defoliation ; or whether 

 some other combination obtains, and the early leafers are 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 as grey as midwinter, but the latter retain their leaves 

 the longer ; we must remember, too, that like many of our trees they 

 get their flowering over before leafing, while in the chestnut the 

 leaves are the first developed. However, as De Candolle remarks, 

 we cannot draw conclusions from stray instances, but must take the 

 mean of researches extending over some time. He accordingly takes 

 the vesiime of four years' observations (1841-44) given by Quetelet (22) 

 in his report on the climate of Belgium. Thirty-eight species or good 

 varieties were observed. De Candolle makes four lists. A, B, C, D. 

 In A he includes the early leafers, in B those with an early leaf-fall. 

 C comprises the late leafers, and D those where the fall is late. 

 Each list contains about thirteen names. Two, Spivaa sorhifolia and 

 the lilac, Syvinga vnlgavis, 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 have a late fall ; two, the walnut 

 and Gleditschia fevox, are common to B and C, having an early leaf- fall 

 though leafing late, and four are late in leafing, and have also a late 

 leaf-fall. It is evident that there is no real connection between the 

 two epochs ; the leaf-fall is independent of the previous budding. 



De Candolle also quotes observations on indi\idual trees as to 

 whether, for instance, any one chestnut which came into leaf early 

 would be earlier or later than others in shedding its leaves. 



In many species, like the horse-chestnut, beech, elm, &c., trees 

 growing side by side, planted at the same time, and subjected to the 

 same external conditions, neither come into leaf nor lose their leaves 

 simultaneously. These facts of idiosyncrasy, he says, are constant. 

 They recur always in the same manner year after year, even when 

 the differences in time are reduced to two or three days. Are the 

 individuals which first come into leaf also the first to lose their leaves ? 

 or is the inverse the case ? Some facts are given for the horse-chestnut, 

 where the difference between individuals is very marked. Of three 

 old trees in the court of a country house at Frontenex, the owner stated 

 that for years they followed the same order of succession at both 



