DORSIVENTRAL SHOOTS. ANISOPHYLLY IN SPERMAPHYTA 113 



the under side l . At a subsequent period the leaf-rows come by torsion 

 to occupy a diagonal position. Species of Strobilanthus supply other 

 examples of anisophylly in this family. 



4. Gesneriaceae. In this family Columnea shows anisophylly feebly 

 in C. Schiedeana, very strongly in C. Kalbreyeri and C. purpurata. It 

 is probable that the two rows of small leaves upon the upper side are 

 suppressed in many Gesneriacae, for example in Klugia, Rhynchoglossum, 

 and others. As a matter of fact I frequently found upon the upper side 

 of the shoot in Klugia a leaf, usually smaller than the lateral leaves, which 

 was evidently a vestige of the upper leaves. 



Anisophylly may also appear on sympodial shoot-systems, which, 

 growing plagiotropously, behave like monopodial shoots. One of the 

 best examples of this is supplied by the flowering plagiotropous shoots 

 of Atropa Belladonna, in which the leaves upon the upper side are much 

 smaller than those upon the flanks, whilst the orthotropous chief shoot 

 is isophyllous. The construction of this shoot conforms entirely with that 

 of Selaginella, Elatostemma, and others, although the mode in which it 

 comes about is different. 



Reviewing the long series of examples of anisophylly to which we 

 have referred above, we are led to the following conclusions: 



1. Anisophylly appears in different degrees amongst the higher 

 plants and amongst the lower plants, and often in different fashion in 

 one genus. 



2. It generally occurs only in plagiotropous shoots, and in the more 

 sharply developed cases appears as an adaptive character which stands 

 in relation to the provision of a surface of assimilation in one plane, or to 

 the projection of the surface of assimilation to the periphery of the 

 crown of a tree ; and the leaves which from their position are less suitable 

 for the formation of this surface show a tendency to reduction and may 

 finally entirely abort. This reduction may be caused directly through 

 the position of these leaves especially in relation to light, but it is in 

 the highest degree probable that relationships of correlation also have an 

 important share in bringing it about. It is sometimes the leaves upon 

 the illuminated side, sometimes those upon the shaded side which are 

 reduced, whilst in Lycopodium complanatum the leaves on both of these 

 sides are reduced together. The strong development of the lateral leaves 

 may have to do with the arrest of the others. 



1 I have observed the same positions in the first leaf-pairs of axillary shoots in Goldfussia isophylla, 

 although these have subsequently leaf-pairs with leaves of equal size. The difference in size of the 

 leaves of the median pair may be explained biologically by the feebler illumination to which the 

 leaf next the mother-axis is exposed. This leaf in one instance was 6-5 cm. long whilst the opposite 

 member of the pair was 11-5 cm. ; in this example the upper leaf of the first pair was also smaller 

 than the under one. The third leaf-pair lying in the vertical plane also showed, but in a less degree, 

 similar features. 



GOEBEL I 



