The wood is so spongy and soft that an axe can be struck in so far with a good blow that there is great difficulty in pulling it out again.  In the dead mowana mentioned the concentric rings were well seen.  The average for a foot at three different places was eighty-one and a half of these rings.  Each of the laminae can be seen to be composed of two, three, or four layers of ligneous tubes; but supposing each ring the growth of one year, and the semidiameter of a mowana of one hundred feet in circumference about seventeen feet, if the central point were in the centre of the tree, then its age would lack some centuries of being as old as the Christian era (1400).  Though it possesses amazing vitality, it is difficult to believe that this great baby-looking bulb or tree is as old as the Pyramids.

The mopane-tree (’bauhinia’) is remarkable for the little shade its leaves afford.  They fold together and stand nearly perpendicular during the heat of the day, so that only the shadow of their edges comes to the ground.  On these leaves the small larvae of a winged insect appear covered over with a sweet, gummy substance.  The people collect this in great quantities, and use it as food;* and the lopane—­large caterpillars three inches long, which feed on the leaves, and are seen strung together—­share the same fate.

   * I am favored with Mr. Westwood’s remarks on this insect as
   follows: 

   “Taylor Institution, Oxford, July 9, 1857.

“The insect (and its secretion) on the leaves of the bauhinia, and which is eaten by the Africans, proves to be a species of Psylla, a genus of small, very active Homoptera, of which we have one very common species in the box; but our species, Psylla buxi, emits its secretion in the shape of very long, white, cotton-like filaments.  But there is a species in New Holland, found on the leaves of the Eucalyptus, which emits a secretion very similar to that of Dr. Livingstone’s species.  This Australian secretion (and its insect originator) is known by the name of wo-me-la, and, like Dr. Livingstone’s, it is scraped off the leaves and eaten by the aborigines as a saccharine dainty.  The insects found beneath the secretion, brought home by Dr. Livingstone, are in the pupa state, being flattened, with large scales at the sides of the body, inclosing the future wings of the insect.  The body is pale yellowish-colored, with dark-brown spots.  It will be impossible to describe the species technically until we receive the perfect insect.  The secretion itself is flat and circular, apparently deposited in concentric rings, gradually increasing in size till the patches are about a quarter or a third of an inch in diameter.

   Jno.  O. Westwood.”