ASYMMETRY OF LEAVES 



127 



in the leaves of plants in very different cycles of affinity, for example 

 in all those which are designated as ' interruptedly pinnate,' such as 

 Solatium tuberosum, species of Geum (see Fig. 81), Potentilla anserina, 

 Spiraea Filipendula, and others. In all these plants individual leaflets 

 lag behind others in their growth, and an advantageous arrangement 

 for making the best use of the light is by this means arrived at, for 

 the small leaflets fill the spaces between the larger ones. Configura- 

 tions similar to this are observable amongst the lower plants also. 



FIG. 80. Euptilota Harveyi. The short shoots are FIG. 81. Geum bulgaricum. Leaf. The terminal 



arranged in a pinnate manner on the long shoots; in lobe very greatly enlarged, the lateral pinnules of 



successive pairs it is alternately the right and left shoot unequal size, mostly in alternating smaller and 



which lags behind in growth. After Cramer. larger pairs. Reduced. 



Fig. Ho is a representation of an alga which exhibits an ' interruptedly 

 pinnate ' long shoot, inasmuch as alternately on the right and on the 

 left a shoot lags behind in the development. The details of the con- 

 figuration are probably regulated by correlation between the several 

 parts concerned the enlargement of some causing others to remain 

 small ; in the leaves of higher plants at least there appears to be no 

 definite rule as to which leaflet remains small, although in some cases 

 position determines this. The leaflets which are turned to the axis in 



