define the difference between primary protonema and secondary protonema

Primary protonema is the first stage in the life cycle of a moss, developing directly from the spore. It consists of creeping, green, branched, and often filamentous structures. Secondary protonema develops from any part of the adult like rhizoids, stems and leaves. Let me explain in detail: The primary protonema produced as a result of spore germination breaks up into small fragments by the formation of some intercalary colourless cells. Each fragment grows into a new protonema. Sometimes filamentous protonema may be formed from any cell of a detached injured portion of any stem, leaf and rhizoid when surrounded by moist air. It is similar in function and behavior to primary protonema and called secondary protonema. 

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