In the present report, the author classified the forage crops into five phenological types according to the season in whicn they grow most vigorously (Table. 1.) The reason why each of them belongs to a particular phenological type may be that it is characterized by its own seasonality. As each crop requires a particular complex of seasonal environments for growth, it cannot thrive vigorously when the latter is not suitable. And there exists no crop which can adapt to all seasons. Therefore for successful introduction of new crop production into acertain district, it is necessary to know the seasonality of the plant. The vernalization treatment may be one of the methods to change the phenological type of the crop. The four seasons here defined are as follows: summer; - the season with temperatures sustained above 20°C, autumn - from 20°C to 5°C, winter - below 5°C and spring - from 5°C to 20°C. Most parts of Japan have distinctive four seasons respectively. Most grasses of foreign origins and some root forages as the swede, for example, are generally difficult to be raised in most districts of japan, except certain regions of especially high altitudes or high latitudes, where the "summer season" as defined above is nearly absent, there remaining only the three "seasens" to which these crops can adapt.