Plant-breeding; comments on the experiments of Nilsson and Burbank . entities, which combineto give it its form and functions. The study of these unitsencroaches upon systematic and comparative sciences, aswell as upon the investigations into the physiology and theevolution of all living beings. All comparison culminatesin the question as to which units are common to the speciesunder discussion, and which units are the causes of theirdifferences. Systematic affinity is reduced to the sameprinciple. It is founded on the community of a more or. Fig. 96. A. The pansv and some of its parents. B. \
Plant-breeding; comments on the experiments of Nilsson and Burbank . entities, which combineto give it its form and functions. The study of these unitsencroaches upon systematic and comparative sciences, aswell as upon the investigations into the physiology and theevolution of all living beings. All comparison culminatesin the question as to which units are common to the speciesunder discussion, and which units are the causes of theirdifferences. Systematic affinity is reduced to the sameprinciple. It is founded on the community of a more or. Fig. 96. A. The pansv and some of its parents. B. \iola lutea grandi-flora. C. Viola tricolor versicolor. D. Viola tricolor lutescens. After Witt-rock. 311 312 PLANT-BREEDING less large number of units, whilst divergence must evidentlybe the result of the occurrence of different units. Thelarger the number of common units, and the smaller that ofvarying constituents, the greater will be the affmity. Wide as are the prospects of solving the most difficultproblems of systematic science and comparative investiga-tions, and tempting as it is to indulge in a discussion of thepossibility of the discovery of their ruling laws on the groundof the principle of units, we must, of course, now limit our-selves to questions more directly concerned with our inquiry. Among these the chief point is, what is to be consideredas a unit? This question is intimately connected with ourmain subject, and sufficient facts are at hand to draw atleast a preliminary sketch. At once it brings us upon theground of
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