Evidence indicates that centrosomes arisede novo in the spermatid mother cells (SMC). Each of the two centrosomes per SMC is composed of a pair of coaxial centrioles which are apposed at their proximal ends and connected only by the central cartwheel portion. Serial transections show that the triplets of the constituent centrioles imbricate in opposite directions. The centrioles later become separated, undergo planar rotation and displacement, and ultimately function as flagellar basal bodies. In structure and behavior the centrosomes and centrioles ofLycopodium are closely comparable to those of bryophytes.