An experiment on the soil heating characteristics of four different types of plastic garden pot, and two different forms of cover, was conducted in six cold frames. In the first stage of the...

An experiment on the soil heating characteristics of four different types of plastic garden pot, and two different forms of cover, was conducted in six cold frames. In the first stage of the experiment, each frame was divided into four quarters, and each different type of pot allocated to one quarter in each frame. Three of the frames were covered with glass, and three with polythene. The design is represented below. After a week, the mean soil temperature of each pot was obtained and then the covers on each frame were changed (Glass→Polythene ; Polythene→G), and a further set of 24 soil temperature measurements were obtained. What is the correct structure for the analysis of variance of the complete set of 48 observations? (From: The Design of Experiments, R. Mead; Ch 14,(4))