Plants on orbit grew more slowly than comparable ground controls. Root growth patterns of plants 8.5 days old from the ground control (A) and flight experiment (B) are shown with mapping overlays. Dotted line marks division between cultivar WS and Col-0. A colored trace was made at each 6 hour increment of growth as each plant grew, out to 8.5 days (A, B). Traces alternated red and blue for clarity. Sections rendered in orange and light blue represent extrapolations for missing individual photographs. Numerical values were calculated for each root and hypocotyl length (grid=13mm), and then the average values for each set of cultivars plotted with respect to treatment (C). Standard deviation was calculated using "n-1" method: Ground control (GC-green bars) - WS: n=11, StDev roots=0.91, StDev hypocotyls=0.70, Col-0: n=7, StDev roots=1.00, StDev hypocotyls=0.60; Flight (FLT-blue bars) - WS: n=13, StDev roots=0.67, StDev hypocotyls=0.80, Col-0: n=7, StDev roots=0.67, StDev hypocotyls=0.40. (D) Traced sections enlarged and the region representing the first 48hours of discernible growth highlighted with a gold bracket. (E) The meristematic zone in roots of ground control (GC) and flight (FLT) plants. Epidermis, cortex, endodermis and quiescent center (QC) are indicated in blue arrows. The gold line along the epidermis cell file from the quiescent center measures 225μm. (F) The elongation zone in roots of ground control and flight plants. The blue frame defines a region of about 225μm along the length of each root from the transition zone into the elongation zone. The cross bars in the rectangle define cell boarders in this area for each root.