Having study of the petrography of the welded tuffs, the author divided the crystalline textures in the welded turfs into two types, i. e., the crystalline texture in the plastical fragments, such as pumice and plastically deformed glass shard, and the texture in rigid glass shard and volcanic dust. Using the theory and the experimental achivement of supercooling crystallization, this paper puts the stress on discussing the genesis of the first type and suggests that it may be formed not by devitrification, but by supercooling crystallization.