* Water content is highly variable: The amount of water in a plant can fluctuate greatly depending on environmental factors like rainfall, humidity, and the plant's physiological state. This variability makes water an unreliable indicator of the plant's actual mass.

* Water is not part of the plant's structural components: Biomass refers to the total dry weight of organic matter in a plant. This includes components like leaves, stems, roots, and fruits, which are composed of carbohydrates, proteins, and other organic compounds. Water, being inorganic, is not a structural component of the plant and does not contribute to its biomass.

* Measuring dry weight provides a more accurate representation of plant growth: By removing water, we obtain a more consistent and comparable measure of the plant's actual growth and development. This information is valuable for studying plant physiology, ecology, and agriculture.

In essence, excluding water from biomass measurements allows for a more accurate and reliable representation of the plant's organic matter, which is the true indicator of its size and growth.