ASYMMETRY OF LEAVES 



121 



dorsi ventral Leguminosae are larger upon the upper side, that of the 

 inflorescence, than they are upon the under side. But the inequality 

 of the leaflets is much more conspicuous in a number of species which, 

 so far as I have been able to examine them in the living state, are all 

 distinguished by the possession of markedly plagiotropous prostrate shoots. 

 These shoots have two rows of leaves and one side of each leaf is turned 

 upwards, the other is turned downwards. The differences here are 

 sometimes so prominent that they have found expression in systematic 

 terminology, and we find the leaves of Indigofera diphylla (Fig. 71, //), 

 of Hosackia subpinnata, and of Anthyllis tetraphylla (Fig. 71, ///), 

 described as ' unilaterally pinnate.' In Indigofera diphylla only one 

 pinnule is present on the upturned side. Anthyllis tetraphylla has two 

 to three large leaflets upon its upturned side, and only one pinnule 

 upon the side downwards 

 directed. The leaves are 

 inserted obliquely on the 

 prostrate shoots so that 

 their upper surfaces are 

 directed obliquely towards 

 the upper side of the shoot. 

 Here we have a case of 

 dorsiventrality quite like 

 that of Begonia, and, as in 

 that genus, the sides of the 

 leaves in the plagiotropous 

 shoots which are reduced 

 are the ones that are feebly 

 illuminated. This pheno- 

 menon occurs indepen- 

 dently in different genera amongst the Leguminosae. I have met with it 

 specially in some Sicilian species. Hedysarum capitatum is very instructive 

 (Fig. 71, /), for in it the leaves of the radial orthotropous leaf-rosette are 

 symmetrical and each leaf bears right and left many equal pinnules ; but 

 in the prostrate plagiotropous shoots which subsequently develop, one or 

 two leaflets are absent from that side of the leaf which lies next the 

 soil. The same may be seen in Vicia Cracca, in which plant also the 

 stipules standing upon the upper side of the shoot are larger than 

 those upon the under side. Hymenocarpus also (Fig. 71, IV) has 

 asymmetric leaves ; and a long series of instances might be quoted. 

 The smaller side of the leaf is partially covered by the lateral shoots 

 or axillary inflorescences if these be present. In Anthyllis tetraphylla 

 I found that the small pinnules which have a tendency to abortion 

 possess an anatomical structure different from that of the large terminal 



FlG. 71. Unequally-sided leaves of different Leguminosar. / Hedvs-' 

 arum capitatum; 77 Indigofera diphylla; 777 Anthyllis tetraphylfa; 

 IV Hymenocarpus circinnatus. 



