Interesting question and experiment! Great initiative! Just one little comment, be careful using the average of percentages, most of the times it doesn't give you an exact number I will give an example:

Plant 1 - 9g of protein in a total of 100 g that means 9% of protein
Plant 2 - 24g of protein in a total of 400g that means 6% of protein , right?
if we take the average of protein percentage (9 + 6) / 200 = 7.5%

However if we do the same with the raw weight of protein / total weight of plants we have a different number, but more precise:

9g+24g = 33g/ (100g+400g) = 6.6%

you can only use the average percentage if the total weight of each plant is the same something like that:

Plant 1 - 9g of protein in a total of 100 g --> 9%
Plant 2 - 24g of protein in a total of 100g --> 24%

9+24 / 200 = 16.5% it is the same calculation in either ways!
Good job anyways =)
!1UP