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Under modern horticultural practice when anyone has been able to secure seed most of which he is reasonably sure will develop into plants of a distinct type different from that of any sort known to him, he has a distinct variety, so that it is not surprising that we should find that American seedsmen offer tomato seed under more than 300 different names, and those of Europe under more than 200 additional, so that we have more than 500 varietal names, each claiming to stand for a distinct sort.
Mendel's law of varietal hybrids is based upon the principle of unit-characters, and the validity of this conception has thus been brought home to many investigators. A study of fluctuating or individual variability, as it was formerly called, is now carried on chiefly by mathematical methods. It is not my purpose to go into details, as it would require a separate course of lectures.
In a book like this it is useless to attempt to give long varietal descriptions even of the sorts commonly listed by seedsmen, since such descriptions would be more a statement of what the writer thought seed of that variety should be rather than of what one would be likely to receive under that name. Production for Canning =Growing for canning= has many advantages over growing for market.
The facts discovered concerning mutations and Mendelian heredity harmonize with the nature of the majority of specific and varietal characters, and with the diagnostic characters of many larger divisions in classification.
Of course it was not possible to ascertain from which variety the plant had really originated, but the reproduction of any one clearly defined varietal mark is in itself proof enough of their origin, and of the latency of the dark brown flower-color in this special case. A still better proof is afforded by a new type of green dahlia.
And as long as we are devoid of empirical means of deciding such questions, it seems useless to go farther into the details of the question of the sterility. It should be stated here however, that pure varietal crosses, when not accompanied by unbalanced characters, have never showed any tendency to diminished fertility.
But to enlarge the range of the varieties this simple and stable form would need to be treated anew, by crossing it with the parent-types. Such experiments however, have miscarried owing to the too stable nature of the unit-characters. This stability and this absence of the splitting shown by varietal marks in the offspring of hybrids is one of the best proofs of unisexual unions.
In the first place the cases in which the differences may occur between parts of the same individual are to be excluded. Dividing an alpine plant into two halves and planting one in a garden, varietal differences at once arise and are often designated in systematic works under different varietal names.
Let us begin with the sharpness of the varietal characters. In this respect varieties differ most obviously from elementary species. These are distinguished from their nearest allies in almost all organs. There is no prominent distinctive feature between the single forms of Draba Verna, Helianthemum or of Taraxacum; all characters are almost equally concerned.
Read in the light of modern ideas on unit characters it is now one of the most important works on heredity and has already widespread and abiding influence on the philosophy of hybridism in general. But from its very nature and from the choice of the material made by Mendel, it is restricted to balanced or varietal crosses.
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