Some kinds are less commonly known, such as the Portuguese Couve Tronchuda, with the ribs of its leaves greatly thickened; and the Kohlrabi or choux-raves, with their stems enlarged into great turnip-like masses above the ground; and the recently formed new race (9/65. 'Journal de la Soc. Imp. d'Horticulture' 1855 page 254 quoted from 'Gartenflora' April 1855.) of the choux-raves, already including nine sub- varieties, in which the enlarged part lies beneath the ground like a turnip.
Although we see such great differences in the shape, size, colour, arrangement, and manner of growth of the leaves and stem, and of the flower-stems in the broccoli and cauliflower, it is remarkable that the flowers themselves, the seed-pods and seeds, present extremely slight differences or none at all. (9/66. Godron 'De l'Espece' tome 2 page 52; Metzger 'Syst. Beschreibung der Kult. Kohlarten' 1833 s. 6.) I compared the flowers of all the principal kinds; those of the Couve Tronchuda are white and rather smaller than in common cabbages; those of the Portsmouth broccoli have narrower sepals, and smaller, less elongated petals; and in no other cabbage could any difference be detected. With respect to the seed-pods, in the purple Kohlrabi alone, do they differ, being a little longer and narrower than usual. I made a collection of the seeds of twenty- eight different kinds, and most of them were undistinguishable; when there was any difference it was excessively slight; thus, the seeds of various broccolis and cauliflowers, when seen in mass, are a little redder; those of the early green Ulm savoy are rather smaller; and those of the Breda kail slightly larger than usual, but not larger than the seeds of the wild cabbage from the coast of Wales. What a contrast in the amount of difference is presented if, on the one hand, we compare the leaves and stems of the various kinds of cabbage with their flowers, pods, and seeds, and on the other hand the corresponding parts in the varieties of maize and wheat! The explanation is obvious; the seeds alone are valued in our cereals, and their variations have been selected; whereas the seeds, seed- pods, and flowers, have been utterly neglected in the cabbage, whilst many useful variations in their leaves and stems have been noticed and preserved from an extremely remote period, for cabbages were cultivated by the old Celts. (9/67. Regnier 'De l'Economie Publique des Celtes' 1818 page 438.)
It would be useless to give a classified description (9/68. See the elder De Candolle in 'Transact. of Hort. Soc.' volume 5; and Metzger 'Kohlarten' etc.) of the numerous races, sub-races, and varieties of the cabbage; but it may be mentioned that Dr. Lindley has lately proposed (9/69. 'Gardener's Chronicle' 1859 page 992.) a system founded on the state of development of the terminal and lateral leaf-buds. Thus:
I. All the leaf-buds active and open, as in the wild-cabbage, kail, etc.
II. All the leaf-buds active, but forming heads, as in Brussel-sprouts, etc.
III. Terminal leaf-bud alone active, forming a head as in common cabbages, savoys, etc.
IV. Terminal leaf-bud alone active, and open, with most of the flowers abortive and succulent, as in the cauliflower and broccoli.
V. All the leaf-buds active and open, with most of the flowers abortive and succulent, as in the sprouting-broccoli. This latter variety is a new one, and bears the same relation to common broccoli, as Brussel-sprouts do to common cabbages; it suddenly appeared in a bed of common broccoli, and was found faithfully to transmit its newly-acquired and remarkable characters.
The principal kinds of cabbage existed at least as early as the sixteenth century (9/70. Alph. De Candolle 'Geograph. Bot.' pages 842 and 989.), so that numerous modifications of structure have been inherited for a long period. This fact is the more remarkable as great care must be taken to prevent the crossing of the different kinds. To give proof of this: I raised 233 seedlings from cabbages of different kinds, which had purposely been planted near each other, and of the seedlings no less than 155 were plainly deteriorated and mongrelised; nor were the remaining 78 all perfectly true.