Originally published in 1727, this groundbreaking work by Stephen Hales is considered one of the most important contributions to the study of plant physiology. In addition to his experiments on plant sap, Hales also conducted groundbreaking research on the properties of air. A must-read for anyone interested in the history of science. This work has been selected by scholars as being culturally important, and is part of the knowledge base of civilization as we know it. This work is in the "public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.