The tillering stage begins with the emergence of lateral shoots (tillers) from the axils of the true leaves at the base of the main stem of the plant. The tillers are formed from the auxiliary buds located at each crown node. Primary tillers form in the axils of the first four or more true leaves of the main stem. Secondary tillers may develop from the base of primary tillers if conditions favor tiller development. A tiller may also develop from the coleoptile node (coleoptilar tiller), but this occurs sporadically and its appearance is dependent on genotype, planting practices, and environmental conditions. At the base of each tiller is a sheath (small leaf like structure) called the prophyll, from which the tiller leaves emerge. The prophyll acts like the coleoptile and protects the auxiliary bud before it elongates its first leaf to become a tiller. Identifying the prophyll, which encloses the base of the tiller, will help differentiate tiller leaves from the leaves on the main stem and from other tillers. Tillering usually begins when the seedling plant has three or more fully developed leaves. Tillers depend on the main stem for nutrition during their development. Once a tiller has developed three or more leaves, it becomes nutritionally independent of the main stem and forms its own root system. - http://www.uky.edu/Ag/GrainCrops/ID125Section2.html

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the Feekes scale of wheat development - http://www.uky.edu/Ag/GrainCrops/Images/2/2.1.JPG