One would ordinarily expect to see such data plotted on a line graph with time (in days) on the horizontal axis and plant height on the vertical axis.
There are a number of other ways it could be done. For example, a bar chart with the height of each bar representing the height of the plant. The botanist could also use something similar where the bar is drawn as a representation of the plant, or where a plant pictorial of a given size is used to represent a specific height. (3 1/2 feet may be represented by 3 full-size icons and 1/2 of another icon stacked on top of each other, for example.)