A Scientist noticed that cattails grew only in swampy parts of his backyard. He decided to try to find out why. He went to the library and found out the following facts Cattails are not found in deserts, Cattails are usually found in many swamps, Cattails sometimes grow in rivers and streams. The scientist thought for a while, then said, think I have figured out the answerCattails need a lot of water to grow" He then went into his yard and dug up 100 cattails. He divided them into four groups. Each group contained 25 cattails. All the groups were grown in the same type of soilthey all received the same amount of light, and they were all kept at the same temperature. Group 1 received 4 of water a day Group 2 received 3 of water a day. Group 3 received 2 mL of water a day. Group 4 received 1 mL of water each day. Every day he went out and measured the plantsAfter 30 days he observed that the plants in group 1 had grown an average of 8 cm. The plants in group 2 had grown an average of 4 cm. The plants in group 3 had grown an average of 2 cm. The plants in group 4 had grown an average of only 1 cm What is the independent variable in this experiment ?