306 VEGETABLE PHYSIOLOGY 
generally accompanied or immediately followed by additions 
to the framework of the growing cells or organs. It is in 
nearly all cases attended by a permanent change of form. 
This is perhaps not so evident in the case of axial organs 
as it is in that of leaves and their modifications, though 
even in them it can be detected to a certain extent. It is 
much more conspicuous in the case of leaves, for the latter, 
as they expand from the bud, have usually a different 
shape from that of the adult ones, and the assumption of 
the mature form is a gradual process, taking place as the 
age of the leaf increases. 
This change of form can be seen not only in the case 
of an organ such as a leaf, but also in that of the indi- 
Fic. 134.—Szcrion or Buspge or Lear, SHOWING THE IRREGULAR CELLS OF 
THE Sponcy MESOPHYLL ABUTTING ON THE LOWER EPIDERMIS. 
vidual cells of which a plant consists. In the apical 
meristem of the root of a flowering plant the cells when 
first formed are almost cubical (fig. 138); after a little 
while we find many of them becoming elongated, and 
ultimately prosenchymatous. Many other cases can be 
noted, particularly the irregularly shaped cells of the spongy 
parenchyma of leaves (fig. 184), the stellate cells of the 
pith of certain rushes (fig. 135), the laticiferous cells of the 
Spurges, &c. 
Growth may, in the light of the considerations just 
advanced, be defined ag permanent increase of bulk, 
attended by permanent change of form. We must not 
assume that every increase of bulk is necessarily growth ; 
