110 



THE BIOLOGY OF A PLANT. 



joins the rliizome. The enlarge- 

 ment is of considerable interest, 

 for it occurs at precisely the 

 point of greatest strain when the 

 leaf is bent bj the wind or other- 

 wise, and must serve to strength- 

 en the stipe. 



It will appear from the fol- 

 lowing description that the plant 

 body exhibits in some measure 

 certain general forms of sym- 

 metry and differentiation which 

 in a broad sense may be regarded 

 as analogous to those occurring in 

 the animal. The rhizome grows 

 only at one end, and in its struc- 

 ture suggests the antero-posterior 

 differentiation of the animal. It 

 also shows a slight differentiation 

 between the upper and lower 

 surfaces, which appears both in 

 the external form and in the ar- 

 ran element of the internal lines. 

 It is furthermore distinctly bilat- 

 eral, a vertical plane dividing it 

 into closely similar halves. These 

 features are, however, far less 

 prominent in the fern than in 

 the earthworm, and in plants 

 they never attain a high degree 

 of development, while in the 

 higher animals they are among 

 the most conspicuous and im- 

 portant features of the body. 

 Fig 45— An entire C)f morc general importance in 

 Sf'^the 'Tllv;s''?s the fern is the repetition of 



young and small, • m i. /i i x 



and a comparison of Similar parts (brauchcs, roots, 



the figure wiUi Fig, , v , ., . i • i 



44TN'iiishowsomeof Icaves) along the axis, wnicii 



tliG cliff crdicGS Tdg- 



tween leares of dif - suffsiests, pei'liaps, a Certain an- 



ferentages. ^^ ' "^ -^ ' 



