THE WALLFLOWER 95 



changes during their development from the cam- 

 bium. The vessels have a much greater diameter 

 than the cambial cells, while the fibres are more 

 elongated. 



If we think the matter over carefully, we shall see 

 that these changes of dimensions in particular cells 

 cannot go on without some disturbance of the original 

 arrangement of the cells. Take a vessel, for instance : 

 as its diameter increases, it has to find room for itself 

 among the surrounding parenchymatous and other 

 cells which do not grow much in diameter. To 

 do this it has to displace its neighbours, and event- 

 ually it comes into contact with many more cells 

 than it touched when first formed from the 

 cambium. 



Next consider the excessive growth in length of 

 the fibrous cells ; each of these when full grown is 

 about twice as long as it was in the cambial condition. 

 In attaining its full length it has to insert its pointed 

 growing ends between its neighbours, and as they, 

 if they are fibrous cells, are all doing the same thing, 

 the ends of these cells have to grow past each other 

 (see Fig. 36,/). All this may happen in a part of 

 the stem which has long ceased to grow in length, 

 so that all the room required must be found by the 

 mutual displacements of the growing cells. To all 

 changes of this kind in which developing cells grow 

 past each other, whether in transverse or longitudinal 

 direction, the name of sliding growth is applied. The 

 meaning of the term is, that the walls of these cells 

 slide upon each other as they grow. 



