Growth is Measurable

At the cellular level, growth is principally a consequence of an increase in the amount of protoplasm. Protoplasm itself is very difficult to measure directly, so in practice one measures some quantity that is more or less proportional to it. Growth is therefore measured by a variety of parameters, some of which are:

• increase in fresh weight
• increase in dry weight
• increase in length
• increase in area
• increase in volume
• increase in cell number

The scale of these increases can be amazing. A single maize root apical meristem can give rise to more than 17,500 new cells per hour, so here growth is expressed as an increase in cell number. In contrast, cells in a watermelon may increase in size by up to 3,50,000 times; here growth is expressed as an increase in the size of the individual cell rather than in their number. …