What are the solid waste products …

1.  Excess water is removed through stomata by transpiration which is the process of removal or evaporation of water.

2.  Plants also get rid of oxygen, a by - product in the process of photosynthesis and carbon dioxide which is the by - product formed during respiration. The plants get rid of these by stomata present in their leaves.

3. Some of the wastes stored in the leaves are removed by the detachment of the leaves itself from  the tree.

4. Waste are also stored in the cellular vacuoles which do not affect the functioning of cytoplasm because of its outer membrane known as tonoplast.

5. Other waste products are stored in resins and gums, especially in old xylem which stops working thereby.
The thing is that the plant have many xylem tissues for the transportation of water and old xylem tissues always get replaced by the new ones.

6. Terrestrial plants excrete some waste into  the soil around them whereas aquatic plants remove the wastes by the process of diffusion.