Depending on the kind of experiments to be performed, plants may have to meet other prerequisites besides responsiveness to "one-shot" photoinduction. Speaking generally, small size at the responsive stage is essential in experiments that involve many treatments and in studies using a spectrograph or any similar equipment where the area irradiated with any wavelength of light is very limited. An experimental approach to any biological process evidently requires its accurate measurement, and progress is often dependent on refinements of the measurement technique. With the progressive refinements of the experiments and measurement techniques, there is an increasing need to control the environmental parameters that is to grow the plants during their whole life cycle in growth chambers or phytotrons, possibly on nutrient solutions and in a controlled atmosphere. Using experimental systems which require a protracted period of induction or using Trapezond tobacco (DNP), the rate of development is often measured by the number of nodes (leaves) preceding the first flower.