Rattan, in his "Flora of California," mentions the fact that Big-root, Megarrhiza Marah, has its dicotyledonous leaf-stems united so that they form a long tube, at the base of which and within, is found the plumule bud, quite under ground. This device, he says, is to protect the bud from insects which would be likely to destroy it.

The plumule, in order to reach the surface, breaks through the side of the tube of the united petioles, and before it gets to the light, leaves one or two axillary buds beneath the ground, in addition to those at the base of the dicotyledonous leaves; so that it has from two to three or five chances of life, should the terminal and exposed leaves with their buds be destroyed.

Something like this, I find obtains with the well-known creeping Tradescantia, the ordinary stem leaves of which are provided with sheathing or tubular petioles that envelop the stem for a distance of half or three-quarters of an inch above the nodes. The axillary bud, the promise of a future stem, it will be clearly seen, can only grow by piercing the tubular petiole, on account of the tightness with which the latter clings to the stem. This it invariably does.

The earlier nodes of the young branch are furnished with sheaths only, its growing point being quite acute, doubtless lor the purpose of more easily making its way through the wall of its tubular cages.

The query naturally comes to one, why this sheathing petiole, and not the ordinary terete, semi-terete or channelled one? Apparently it is not given for the especial well-being of the new stem; but may be provided to strengthen the enclosed internodes against the weight of axillary branches, which shoot forth very quickly after the appearance of each stem leaf.