Species and Varieties, their Origin by Mutation
Lectures delivered at the University of California 1904
By Hugo DeVries, Professor of Botany in the University of Amsterdam
As an illustrative example I will take the genus Canna. Originally cultivated for its large and bright foliage only, it has since become a flowering plant of value. Our garden strains have originated by the crossing of a number of introduced wild species, among which the Canna indica is the oldest, now giving its name to the whole group. It has tall stems and spikes with rather inconspicuous flowers with narrow petals. It has been crossed with C. nepalensis and C. warczewiczii, and the available historic evidence points to the year 1846 as that of the first cross. This was made by Anneé between the indica and the nepalensis; it took ten years to multiply them to the required degree for introduction into commerce. These first hybrids had bright foliage and were tall plants, but their flowers were by no means remarkable.
Once begun, hybridization was widely practiced. About the year 1889 Crozy exhibited at Paris the first beautifully flowering form, which he named for his wife, C. ‘Madame Crozy’. Since that time he and many others, have improved the flowers in the shape and size, as well as in colour and its patterns. In the main, these ameliorations have been due to the discovery and introduction of new wild species possessing the required characters. This is illustrated by the following incident. In the year 1892 I visited Mr. Crozy at Lyons. He showed me his nursery and numerous acquisitions, those of former years as well as those that were quite new, and which were in the process of rapid multiplication, previous to being given to the trade. I wondered, and asked, why no pure white variety was present. His answer was "Because no white species had been found up to the present time, and there is no other means of producing white varieties than by crossing the existing forms with a new white type."
Comparing the varieties produced in successive periods, it is very easy to appreciate their gradual improvement. On most points this is not readily put into words, but the size of the petals can be measured, and the figures may convey at least some idea of the real state of things. Leaving aside the types with small flowers and cultivated exclusively for their foliage, the oldest flowers of Canna had petals of 45 mm. length and 13 mm. breadth. The ordinary types at the time of my visit had reached 61 by 21 mm., and the "Madame Crozy" showed 66 by 30 mm. It had however, already been surpassed by a few commercial varieties, which had the same length but a breadth of 35 mm. And the latest production, which required some years of propagation before being put on the market, measured 83 by 43 mm. Thus in the lapse of some thirty years the length had been doubled and the breadth tripled, giving flowers with broad corollas and with petals joined all around, resembling the best types of lilies and Amaryllis.
Striking as this result unquestionably is, it remains doubtful as to what part of it is due to the discovery and introduction of new large flowered species, and what to the selection of the extremes of fluctuating variability. As far as I have been able to ascertain however, and according to the evidence given to me by Mr. Crozy, selection has had the largest part in regard to the size, while the color-patterns are introduced qualities.
[Note: according to Monsieur Anneé in "Le Canna", 1864, C. nepalensis was just a synonym of C. glauca. ]