Drummond says, that "the bulb is renewed every year in the centre of several layers of bark-like substance, one of which layers is added every year by the decay of the old bulb. If the young bulb is dissected at the time when the plant is in flower, the layer of fibrous substance, which afterwards becomes the covering, is easily perceptible; it terminates in a point, which the following season becomes a root, and another root is produced from the bottom of next year's flower-stalk. In planting these roots the fibrous substance should not be removed, or the plant will not thrive. The layer can be easily traced back for ten or twelve years, and I have no doubt that many of these Orchidaceæ have continued to flourish in half a square inch of earth for ages."
"These coated species grow mostly on the exposed sides of hills, where the soil is a strong loam, mixed with a large proportion of gravel, and where their numerous coats must be of the greatest use in protecting their roots from the excessive heat of the summer sun. All the time they appear aboveground the weather is seldom warmer than in England in the month of May." Such plants as Caladenia (fig. 3 & 3*) deviate a little from this manner of growth, their roots forming knots, analogous to those on the roots of Arrhenatherum avenaceum, and ought, Mr. Drummond thinks, to be considered rather as reservoirs of nourishment, to enable the plant to flower and perfect seeds, than as true bulbs or buds.
"Young plants may be produced by dividing the roots; but they spring from the joints between the swellings of the root. One of these swellings, or tubers, is produced annually, or more than one when the root becomes forked, as it sometimes does." This description applies only to Glossodia and Caladenia, the species of all which seem to have the same natural habit.
Another plan of growth is to form a bulb at the end of long woolly roots, as in Drakæa (fig 5 &: 7), Caleana (fig. 4), and Leptoceras (fig. 8); and this sometimes takes place in an excessive degree, as is shewn at fig. 6, where a a are the new bulbs, and b the mother which brought them forth. Mr. Drummond has traced them in one species for more than a foot.
The same collector speaks thus of what he supposes to be a Diuris, and which, from the figure given (9), seems to be of that genus; but the description does not apply to it.
