Assigning a visual volume score to vegetation is a nondestructive method of obtaining measures of biomass. The volume score is the volume of space occupied by the plant computed according to an...

Assigning a visual volume score to vegetation is a nondestructive method of obtaining measures of biomass. The volume score is the volume of space occupied by the plant computed according to an extensive set of rules involving different geometric shapes. The accompanying data on volume scores and biomass dry weights for grasses were obtained for the purpose of developing a prediction equation for dry weight biomass based on the nondestructive volume score. (Data were provided by Steve Byrne, North Carolina State University, and are used with permission.)

Use a polynomial response model to develop a prediction equation for Y = (dry weight)^½
on X = 1n(volume + 1). What degree polynomial do you need? Would it make sense in this case to force the origin to be zero? Will your fit to the data still be satisfactory if you do?