In southeastern Asia the grassland of Imperata cylindtica, scattered within the tropical forests are called Alang-alang, according to the term of Malayan natives. The development of such a landscape is not due to the natural phenomena such as forest-file or cyclones, as it is often believed Under tropical climate, the regrowth of forest is so rapid that the destruction of forest is not an impetus strong enough to permit the making of Alang-alang. There must be some external. forces that work to maintain the destructed forest landscape against the regrowth of big trees. In this paper the author's conclusion through his own observations in Farther India and Malay Archipelago is as follows:……1. The distriibution of volcanic soil is an important cause to form the grassland. 2. Alang-alang is more frequently formed through the abandonment of once cultivated land. This kind of abandonment often occurs through natives' superstition prevalence of epidemics, or through changes of economic coreditions. This last one often occurs here where the conciderable proportion of agriculture is occuied by the plantation which, more than other form of agriculture, depends upon the condition of world market. 3. For the preservation of this landscape, the natives' costom to burn the grass. periodically to quicken the new growth of grass for their cattle and to keep wild beasts off, plays an important part.