Cover illustration: The protonema of the moss Physcomitrella patens comprises two cell types: caulonema and chloronema. Caulonemal cells (top picture) are long and narrow and have all the characteristics of tip growing cells including a clear tip body and a very rapid growth rate. Chloronemal cells (middle picture) grow slowly, contain many chloroplasts and lack a distinct tip body. Nevertheless, the analysis of the movement of fluorescent beads attached to the surface of expanding chloronema showed that these cells (bottom pictures) elongate by tip growth like caulonema. (See Menand et al., pp. 1843–1849.)
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