Plant-breeding; comments on the experiments of Nilsson and Burbank . ecies which are observed in the is a question of purely scientific interest. Two possibil-ities offer themselves. Either the high degree of variabihtyis old and the same elementary types which are now existinghave already existed for centuries, or the production of newvarieties is steadily going on, afforchng a cause of increasingvariabihty or, at least, of a changing group of units. In thefirst case the mixtures would be constant and only exposedto accidental losses by the crowding out of some of theirrarer consti
Plant-breeding; comments on the experiments of Nilsson and Burbank . ecies which are observed in the is a question of purely scientific interest. Two possibil-ities offer themselves. Either the high degree of variabihtyis old and the same elementary types which are now existinghave already existed for centuries, or the production of newvarieties is steadily going on, afforchng a cause of increasingvariabihty or, at least, of a changing group of units. In thefirst case the mixtures would be constant and only exposedto accidental losses by the crowding out of some of theirrarer constituents. In the latter case, however, the processmust be assumed to be a slow one, and the existence ofhundreds of types is no proof of a high degree of change-ability. This conclusion will easily be arrived at from thefollowing considerations. The ever-occurring crosses must 82 PLANT-BREEDING have the effect of rupidh* increasing the number of types,even if ordinary mutal)ility is slow in prockicing new , by this crossing, each new unit will become united. Fig. 23. Stiff-branched Svalof oats. with many of the existing types and, in the end, perhaps,with all of them. In this way, the production of one reallynew unit will tend to double the number of the existingtypes, and, in tlie cases of many ,L:ardeii llowers, where such NILSSONS DISCOVERY 83 crosses have been artificially made, the fact that one newcharacter by this means yields a very large number of newvarieties is universallv known, and one of the most ordin-
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