RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. 



421 



portions of the leaf separated by the midrib are very unlike. The dissimilarity is 

 seen principally at the base of the leaf — it looks as if a piece had been taken out 

 of one side, or as if the leaf had there been cut off obliquely (see fig. 110). The 

 correct explanation of this want of symmetry will perhaps be arrived at most 

 easily by supposing the suppressed portion to be completed, or in other words, 

 let us suppose the smaller half to be just as large and well-developed as the 

 other. It is then evident that the added portions would be covered over by the 

 neighbouring leaves, and consequently they would be deprived of light, and that 

 in these parts, therefore, the chlorophyll-bodies, if present, would not be able to 



i'ig. 111.— Mosaic of 



of unequal size. 



1 Projecting branch of Deadly Nightshade {Atropa Belladonna) looked at from { 



seen from above. 



B. 8 Selaginella Helvetica, 



carry on their activity. These portions of the foliage -leaves would accordingly 

 be superfluous, and it is foreign to the ways of plants to manufacture so much 

 leaf-tissue for no purpose whatever. Plants never form anything which is 

 superfluous and useless; in the construction of all the organs the principle 

 apparently is to attain the greatest possible result with the least amount of 

 material, and to utilize the given conditions, above all, the existing space, as far as 

 possible. 



Yet another phenomenon, viz. the unequal size of adjoining leaves on the same 

 plant, must be considered from this point of view. It must strike everyone who 

 looks down upon a horizontally-projecting branch of the Deadly Nightshade 

 {Atropa Belladonna, see fig. Ill ^), that larger and smaller leaves are here arranged 

 in quite a peculiar manner. The larger leaves stand in two rows, and in virtue 

 of their shape it happens that, between every two, gaps are left near the stem. 



