9 6 



RELATIONSHIPS OF SYMMETRY 



with reference to the earth's radius, which may lead to a diminution of 

 the leaf-rows, altogether apart from the dorsi ventral ity. 



Keeping this in mind, we note the following examples : In Castanea 

 vesca the leaves stand upon the chief axis of the seedling and upon 

 the stronger stool-shoots in a 2 / 5 phyllotaxy ; on the lateral shoots 

 the phyllotaxy is l / 2 . In the seedling of Corylus Avellana the 

 phyllotaxy is l / z and the lateral buds of its axis have a distichous 

 phyllotaxy ; strong shoots of the hazel, such as are often formed at the 

 base of the shrub, are orthotropous and then show a radial phyllotaxy 

 of ] / 3 . Species of one and the same genus may behave differently. 

 All the shoots on the European species of birch have a spiral phyllotaxy, 

 but in Betula lenta and Betula nigra l only the orthotropous chief shoots 

 exhibit this, the lateral shoots have distichous leaves, and this is also the 



FIG. 52. Tilia parvifolia. Transverse section through a shoot-axis. To the left a leaf with an axillary shoot, 

 v,, z>2 its prophylls ; to the right in dotted outline is indicated the transverse section of a succeeding leaf with its 

 axillary shoot. The leaves converge towards the lower side, but not so strongly as is shown in the figure. 



case in Alnus viridis 2 . Analogous cases amongst succulent plants, which 

 are very instructive, will be spoken of in the chapter upon the influence 

 of gravity (p. 219). 



If now we imagine the radial chief axis in the trees to which 

 I have referred to be limited only to its seedling state, we should obtain 

 the condition already mentioned as occurring in Carpinus, Ulmus, Tilia, 

 and others which in their later period of growth consist of distichous 



1 See Doll, Flora von Baden, p. 527. Of herbaceous plants Callisia delicatula, one of the Com- 

 melinaceae, is the only one I mention here ; it has a f phyllotaxy on the chief shoot and | phyllotaxy 

 on the lateral ones. The lateral axes show their dorsiventrality in that the leaves are approximated 

 towards the under side and are oblique. See Kolderup-Rosenvinge, UndersySgelser over ydret Faktorers 

 Indflydelse paa Organdannelsen hos Planterne, in Vidensk. Medd. Naturh. Foren. i Kjobenhavn, 1888, 

 p. 57. Other species of Coinmelinaceae, for example, Cyanotis kewensis, Clarke, behave in like 

 manner. 



* With reference to Alnus gl.iuca. see Hofmeister, Allgemeine Morphologic, p. 609. 



