42 J. Chem. Inf. Model., Vol. 50, No. 1, 2010 CLARK Figure 7. Orientation patterns for 9 root fragments. The numbers indicate how many structures are contained in each group. Hydrogen bond donors are tinted blue; acceptors are tinted red. Figure 8. (a) Single root fragment and a selection of its immediate descendents. (b and c) Selected child of the root fragment and a selection of their descendents. the molecules which are represented by each node, which can be used to identify trends in activity data. Figure 8 shows several subsets of the fragmentation hierarchy for a data set compiled to show activity against various species of DHFR, using the data set described in the previous section.9 Figure 8a shows a single root fragment, and several of the immediately descended fragments. Each of the nodes provides an indication of the activity values against Pneumocystis carinii DHFR of the constituent molecules by means of a colored pie chart display at the