70 RELATIONSHIPS OF SYMMETRY 



of plagiotropous shoot-generations. It is thus in the beech, the lime, and 

 the elm. Orthotropous shoots are formed in these trees only in the 

 young condition in germination, and they differ therefore in configura- 

 tion from the plagiotropous ones which appear later. The latter are 

 distichously-leaved and dorsiventral. The seedlings of the beech 1 are ortho- 

 tropous, the first two leaves being placed at right angles to the cotyledons, 

 and with them the seedling plant usually closes its growth for the season ; 

 occasionally however a third leaf appears over one of the cotyledons. The 

 terminal bud of the first annual shoot is however already dorsiventral-. 

 Ulmus possesses in its first year decussating whorls of foliage-leaves, 

 alternate distichous phyllotaxy appears only in its second year and on 

 the first lateral shoots of the axis of the seedling which has limited growth. 

 The seedlings of the lime are radial with a two-fifths phyllotaxy. All 

 these trees produce later dorsiventral distichously-leaved plagiotropous 

 shoots only, nevertheless there is built up a stem with a radial crown, 



FIG. 30. Transverse section of a twig of a lime-tree. One lateral bud with distichous leaves has been cut 

 through ; its plane of symmetry does not coincide with that of the mother-shoot. 



such as exists in other trees from the beginning. This comes about in this 

 way : the planes of symmetry of the generations of shoots which follow 

 one upon the other do not coincide (see the diagram in Fig. 30) ; in 

 the shoots then which grow in the main erect, the stem, composed as it is 

 of different generations, will have a radial construction, whilst on the 

 shoots growing more horizontally the plane of symmetry of their dis- 



1 According to Doll, Flora von Baden, p. 537, the phyllotaxy of the seedling plant of Fagus 

 sylvatica and of Carpinus Betulus, as well as of Ulmus, is partly spiral, partly decussate. The seed- 

 lings of Ulmus which I examined, either U. campestris or U. effusa, had altogether decussate 

 phyllotaxy and the leaves were not asymmetric as they are on the later plagiotropous shoots. 



2 See Koldemp-Rosenvinge, Unders0gelser over ydre Faktorers Indflydelse paa organdannelsen hos 

 Planterne, in Vidensk. Medd. Naturh. Foren. i Kjobenhavn, 1888. 



