Question

Why do you think that tracheids evolved before vessel members?

Answer 1

Vessel are the part of fluid conducting tissues i.e. xylem. These are present in the flowering plants but absent in gymnosperms. It is the assumption that vessel are evolved from the tracheids after losing their end wall. During the development phase of vessel the end walls get pitted and disappear. This disappearance is also linked with breakdown of cellular protoplast.   

Tracheids can be found in all plants where vessels are found in specialized plants i.e. angiosperms. So it can be concluded that tracheid are basic structure of fluid conducting system where vessel is advanced one found in few type of plants