Instruct: Classify Amazon reviews into positive or negative sentiment
Query: An Outstanding Reference and Very Useful

Overall this is an outstanding reference for anyone wanting to learn the elements of grass identification. It is not intended as a book for identifying any particular grass. I used it for 20 years in a class I taught in Agrostology (Grass Taxonomy), and especially for beginners it was very useful for learning grass structures needed for identification, and to a lesser degree for structures of plants like sedges. Grasses are beautiful, but incredibly complex, and it takes many books and years to be really comfortable with them. Books such as Harrington's smooth the way, and make the task of learning grasses fun. Highly recommended :-)