Consider the following statements with reference to criterion/ criteria used in the classification of plants in the Engler and Prantl's system. I. The families were arranged according to the increasing complexity of flower and fruit. II. In flowering plants, absence of perianth was considered as a primitive character. III. Monocots were considered to be more primitive than dicots. IV. Unisexual flowers were derived from bisexual flowers. Which of the abovementioned statements are correct?