A third peculiarity is exhibited in the globular forms of Melocactus and Mamillaria, in the structure of the wood, which differs entirely from that of the common ligneous plants. Common wood, for example that of the poplar, is composed of long _wood-cells_, the walls of which are quite simple and uniform, and of cells containing air, the so-called _vessels_, the walls of which are very thickly beset with little pores. Wholly unlike this, the wood of the cactus, above-mentioned, exhibits only short, spindle-shaped cells, inside which wind most elegant spiral bands, looking like little spiral staircases. Lastly, the hair, spines, etc., situated in the places of leaves, deserve a special mention. Generally speaking, three forms may be distinguished, all three usually occurring together on the same spot. The first are very flexible, simple hairs, which form a little flat, soft cushion; among these is found a bunch of longish but thin spines. These it is chiefly which, on account of their peculiar structure, make the careless handling of the cactus plants so dangerous. These little spines are very thin and brittle, so that they readily break off, and are covered with barbed hooks directed backward from the point. When touched, a whole bunch penetrate the skin; if an attempt is made to draw them out, the separate spines break in the skin, and the fragments pierce in other places; when the hand is drawn over them, they catch in, and an insufferable itching, terminating in a slight inflammation, spreads over all the parts which have been touched. The Opuntia ferox is especially remarkable for these spines, whence its name, the _savage_. Among the hairs and smaller spines arise very long and thick spines, in different form and number, which give the best characters for the determination of the species. In some these are so hard and strong that they even lame the wild asses which incautiously wound themselves, when kicking off the spines to reach the means to still their thirst. In Opuntia Tuna, which is the kind most frequently used for hedges, they are so large that even the buffaloes are killed by the inflammation following from these spines running into their breasts. FUNGI --HUGH MACMILLAN