Explanation

[Solution from source] Auxospores are formed by many diatoms to restore full cell size after repeated divisions shrink the silica frustule. Hormocysts are thick-walled, multicellular perennating filaments made by only a few filamentous cyanobacteria (such as Westiella). So the order is diatoms first, then cyanobacteria, and hormocysts are restricted to a few. Answer (1).