QUANTITATIVE INFLUENCE OF CORRELATION 209 



exhibit transformation or reduction, for example, in Berberis in which the 

 leaf-thorns have short leafy twigs in their axils, and also in Pinus where the 

 leaves on the long shoots are reduced to scale-leaves. 



Long ago, de Candolle l referred these phenomena to the withdrawal 

 by the leaves of the ' sap ' from their axillary buds. Wiesner 2 advanced 

 the analogous explanation that the older and more strongly transpiring 

 parts, here the axillant leaf of the bud, withdraw the water from the 

 younger parts and therefore hinder the sprouting of the shoot. A similar 

 explanation has been given of the abortion of the apex of the annual 

 shoots of Ulmus, Fagus, Carpinus, Tilia, and other trees; in these plants 

 the leaves gradually diminish in size towards the point of the shoot the end 

 of which finally withers and falls off, and this non-persistence of the terminal 

 bud has been ascribed to the abstraction of water by the older parts. In 

 my view other factors are also concerned in these phenomena. 



Correlation with other buds is also a point that must specially be con- 

 sidered in connexion with the development of a bud. Without defoliating 

 an annual shoot which is still growing, we can cause its buds to shoot out by 

 removing its apex : the buds which are nearest the cut surface then shoot 

 out, as has already been explained, those which lie towards the base of the 

 shoot become arrested in their development, they remain undeveloped or 

 grow out into short twigs. To this point I shall refer later. That the 

 buds which remain undeveloped may be of subsequent use in the event of 

 injury to a tree has already been stated. The provision of many plants in 

 this respect is well shown in seedlings of Juglans regia. Here a large series 

 of buds placed one above the other up to as many as eight is found above 

 the axil of the cotyledon although there is usually only one bud in the axil 

 of each of the other leaves. No one of these numerous buds develops into 

 a twig in the normal and undisturbed development of the seedling, and 

 after some years they are no longer visible. This arrest is not brought 

 about by an ' abstraction ' of the sap by their subtending leaf, because here 

 the cotyledons remain hypogeal ; it is due to all the available food- 

 material being devoted to the development of one terminal bud by which 

 the stem increases in length. If this bud be destroyed whilst the lateral 

 buds are still capable of development, that is in the first or second year of 

 the plant, then one or more of the lateral buds will shoot out and the 

 further development of the seedling is secured. Many cases of develop- 

 mental arrest on vegetative shoots and on flowering shoots can be traced 

 to correlation of growth. 



This holds good also for leaves and parts of leaves. The size which the 

 leaves attain is much greater when each single leaf has a plentiful supply 



1 De Candolle, Physiologic vegetale, p. 767. 



2 Wiesner, Der absteigende Saftstrom und dessen physiologische Bedeutung, in Botan. Zeitung, 

 1889, p. i. The literature is not given in this paper. 



GOEBEL P 



