A structure called the coleoptile, essentially a part of the "cotyledon", protects the young stem and plumule as growth pushes them up through the soil.
On others, he placed blocks containing the chemical, either centred on top of the coleoptile to distribute the chemical evenly or offset to increase the concentration on one side.
Their experiments showed that the coleoptile of a young grass seedling directs its growth toward the light by comparing the responses of seedlings with covered and uncovered coleoptiles.