Etiolation is the development of plants or plant parts in the absence of light. This results in such characteristics as small unexpanded leaves, elongated shoots, and lack of chlorophyll, resulting in a yellowish or whitish color.
Etiolation in bean. Notice that the hypocotyl hook does not open in the dark.
Stock plant etiolation is one technique that can be used to induce rooting in difficult to root cuttings. Illustrated to the right are etiolation tents used on a small scale to treat stock plants so the resultant cuttings are easier to root.
This is done in early spring just as growth begins and the cuttings are handled as softwood cuttings under mist propagation.
Lilac being etiolated by covering plants with opaque plastic. From B.H. Howard, East Malling, UK.