In Plants and Animals. 79 



A division of the zone into segments would also seem 

 to operate in plants. The meridional lines on the surface 

 of the echinocactus may have the same significance as 

 the ambulacral lines on the surface of the sea-urchin. 

 The separation of the original cups of the bud into 

 leaves or petals or stamens is an undoubted case of seg- 

 mentation : and, not less plainly, so also is the dehis- 

 cence of the fruit in certain directions. 



In both cases the facts are sufficiently conclusive to 

 justify the conclusion that segmentation of the zone in 

 the course of development is a phenomenon common to 

 plant and animal. 



The analogy between plant and animal holds good, 

 also, when an attempt is made to trace it in the opposite 

 direction, with a view, that is, to realize the way in which 

 various zones are united to each other. 



On making a horizontal section of a succulent melo- 

 cactus the slightly formed woody zone which has its 

 place in the midst of the softer structures is found to be 

 strengthened here and there by fibres proceeding from 

 the rudimentary buds on the surface of the plant, 

 which, as Du Petit Thouars pointed out long ago, are 

 really the roots of these buds. In point of fact these 

 buds root themselves in the plant-mother in precisely the 

 same way as that in which the plant-mother roots her- 

 self in the earth. And as it is with these buds so it is 

 with all other buds, though seldom so obviously. The 

 roots of the buds, therefore, have much to do in keeping 

 the different parts of the plant-mother together. They 

 act like commissures : they are, as it would seem, the 

 only parts so acting ; and this is the point to which 

 attention is now directed particularly. 



In animals, also, there are not a few facts which seem 

 to Doint to the same conclusion. One and the same 



