This chapter is devoted to the quantitative description of a number of shoot-apical systems. It does this in considerable detail, perhaps with tedious detail. Nevertheless, it supplies the bulk of the evidence upon which the thesis of the book is built, and all but the sections on wheat and subterranean clover are published for the first time. Many will be content to treat the chapter as resource material, and use it to check the claims made elsewhere. Others with a special interest in the test plants will perhaps persist, and still others will find it helpful to the planning of work on other systems.

Some attempt has been made to reduce the tedium by relegating the description of methods and procedures to the Appendix. The systems described have been studied over a period of some fifteen years so there is an unavoidable unevenness of purpose and treatment. The wheat apex was the first to be studied, followed by that for clover – a dicotyledon. Flax followed because of a growing interest in phyllotaxis for its own sake. The same may be said for Eucalyptus, as an example of the decussate condition, and the less extended studies of tobacco, lupin and cauliflower aimed to fill in some obvious gaps in our knowledge of spiral systems. Finally, Ficus was selected as an extreme example of a tightly packed apex, which could be expected to be subject to physical constraint during its long period of development.

Controlled environments are almost essential for studies of growth rate in plants, and the temperature and light regimes used in these studies were selected to give near-optimal rates of growth in each case.