GROWTH 305 
going on in its tissues, the resulting plant weighs much 
less than the original potato. 
This difference is however rather apparent than real. 
We shall see that the actual growth, as well as the manufac- 
ture of new cells, is confined to certain 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 
the other hand, necessarily 
imply any growth. The 
deposition of reserve mate- Fie. 193 Tanpmnnewar: SECTION OF 
rials in many geeds does Youne Root, sHowine StRucTURE oF 
Growine Point. x 20. 
not take place to any great 1, zone of cell division; 2,region of greatest 
extent till their mature growth; 3, region of complete differen- 
dimensions are reached, one 
and growth is therefore completed. It involves, however, 
a considerable increase of weight. 
Growth is in the strict sense, then, always associated 
with the formation of new living substance, and is very 
20 
ro 
ELIT ELI. 
Sie 
ceERnRne 
se 
> 
