water from a hose, the contact of the nozzle or of the spout of a sprinkler, the careless brushing of the sleeve or the hand against the dirt, may result in the transference of seeds and the vitiation of the results of years of labor and care, especially if a complicated series of tests is under way.
Having observed all the above precautions, the seeds finally sprout in due time, unfold the seed-leaves and begin development. The remote possibility is to be taken into account that the parental individuals may have been hybrids and that this, the second, generation may illustrate the resolutions, combinations, dominancy and recessivity of the ancestral characters. If, however, no such differentiation be encountered the observer has before him a progeny which by the multiplication of his seed-pans may be made to include as many individuals as might be found in a great geographical area during any season. The accurate examination of this material, and of that offered by succeeding generations may reveal evidence of the highest interest, bearing upon various problems in heredity. It is to be noted that if guarded seeds were not obtained for the beginning of the test, the more important work must await the second generation under culture for its beginning.
In even the first examination of the progeny of any physiologically unified strain it will be evident that some diversity of form and appearance is present. This variability is generally of the fluctuating type, that is, the entire number of individuals present may be arranged in a series with respect to any quality. Thus, if the one with the narrowest leaf-blades and the one with the widest are placed at opposite poles, the
