GROWTH 311 
moisture by transpiration, and of carbon dioxide as a 
consequence of its respiration or the katabolic processes 
going on in its tissues, the resulting plant weighs much 
less than the original potato. 
This difference is how- 
ever rather apparent than 
real. We shall see that 
the actual growth, as well 
as the manufacture of 
new cells, is confined to 
certam regions. In these 
regions there is a consider- 
able increase in bulk and 
weight, but as the materials 
which are used for the pur- 
poses of this local growth 
are derived from substances 
stored up in the body of 
the tuber, the latter, the 
greater part of which is 
not at any time the seat 
of the growth, diminishes 
in weight and size to such 
an extent as more than to 
counterbalance the gain in 
the growing regions. Hence 
the whole plant weighs less 
than the tuber, though con- 
siderable growth may have 
taken place. 
Mere increase of weight 
in an organ does not, on 
aon a 
Ss — oe = 
De ao ee 
Youre Root, SHOWING STRUCTURE OF 
Growre Port. x 20. 
1, zone of cell division; 2, region of 
greatest growth; 3, region of complete 
differentiation. 
the other hand, necessarily imply any growth. The depo- 
sition of reserve materials in many seeds does not take place 
to any great extent till their mature dimensions are reached, 
and growth is therefore completed. 
It involves, however, 
a considerable increase of weight, 
