A student investigated the effect of wind speed on the rate of transpiration. The student used the flowering plant Japanese spiraea, Spiraea japonica. The student used the apparatus shown in Fig. 1.1 to measure the rate of transpiration. [Figure 1.1] To set up the apparatus the student: • obtained a Japanese spiraea plant growing in a container of soil • added 200 cm³ of water to the soil • placed a plastic bag around the container of soil to prevent water loss from the soil • placed the plant and container on the balance • switched on the fan to a low setting. The roots of the Japanese spiraea plant absorbed water from the soil. Water was carried in the xylem and water vapour was lost by transpiration from the leaves of the plant. This caused the reading on the balance to decrease during the investigation.