Companion cells are closely associated with

1. Sieve elements

2. Vessel elements

3. Trichomes

4. guard cells

Transport of food material in higher plants takes place through -

1. Transfusion tissue

2. Tracheids

3. Sieve elements

4. Companion cells

A common structural feature of vessel elements and sieve tube elements is :

1. thick secondary walls

2. pores on lateral walls

3. presence of P-protein

4. enucleate condition