n.下层(基础；胶层；基层)
The story has a substratum of truth. 这故事有事实的基础。
The soil has a substratum of rock. 这土壤下面有层石头。
"The Old Yue substratum"in south dialects of Chinese comprises different types. 南方汉语里的“古越语底层”有不同类型的情况。
There was in the woman a substratum of the brute, and in the man the material for a blackguard. 那妇人就具有做恶婆的本质，那男子也是个无赖的材料。
Effect of Culture Substrata on Seedlings of Rare and Endangered Plants from Limestone Regions. 不同栽培基质对石山珍稀濒危植物苗期生长的影响。
The typical sampling devices for BBL fauna in dude sledges (for soft bottom) and traps (for hard substrata). 底边界层动物的采样装置主要包括滑橇式和陷阱式两种类型。
adj.基础的；基本的；根本的
