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Several automated systems have bee reported which use modifications of the line-intersect method to accurately estimate root length; however, most of these systems are relatively expensive to construct. The system described here employs an X-Y plotter, a 2 x 2 slide projector, and a fiber optic photodiode to determine intersections between projected images of a root system and grid pattern traced by the light sensor, which is mounted in the pen of the X-Y plotter. With adequate shielding to eliminate false counts, the system reproduced manual counts (r2=0.9999) for white sewing thread, carpet thread, and 0.14-mm-diam. wire. When calibrated against known lengths of root, an r2 of 0.8265 was obtained. The low r2 value was caused by lack of contrast between the background and the images of small roots on the film being used. When roots were stained with methyl violet to increase the contrast, the r2 value increased to 0.9774 with an SE of ±20 cm. Several automating features will be discussed.