792 Bulletin American Museum of Natural History. [Vol. XXIII, 



fast as this is consumed it is renewed with fresh material. The larvae from 

 time to time perforate this plug and clean out their cells, pushing out the 

 pellets of excrement through the opening. This debris is promptly removed 

 by the mother and the opening agaii) sealed with ambrosia. The young 

 transform to perfect beetles before leaving their cradles and emerging into 

 the galleries." The ambrosia of Ptewcydon "is moniliform and resembles 

 a mass of pearly beads. In its incipient stages a formative stem is seen, 

 which has short joints that become globular conidia and break apart. Short 

 chains of cells, sometimes showing branches, may often be separated from 

 the mass. The base of the fungus mass is stained with a tinge of green, 

 but the stain on the wood is almost black." 



In Xyloterus retusus Lee, which lives in the broad-toothed aspen (Popu- 

 hs grandidentata) of the northern States, and is the largest of our ambrosia 

 beetles, still other peculiarities are observable. "Several pairs of the beetle 

 unite in colonies having a single entrance, but each family occupies its own 

 quarters, consisting of one or two branch galleries. The galleries do not 

 penetrate deeply into the heart-wood. Each female attends her own brood, 

 which are raised in cradles extending upward and downward at right angles 

 to the main passage-way. She feeds the young with a yellowish ambrosia 

 grown in beds in the neighborhood of the cradles. The mouth of each cradle 

 is constantly kept filled with a plug of the food fungus. The ambrosia 

 consists of oval cells which form upright sticks resembling some forms of 

 styliform ambrosia, but they do not branch and are capable of being broken 

 up into beadlike masses without losing their vegetative powers. Although 

 the color of the fungus is yellowish, the galleries are stained intensely black." 



The foregoing account of the ambrosia beetles suggests a number of 

 intricate and important problems for future investigation. That these 

 insects have developed unusually advanced social habits for Coleoptera is 

 certain. It is also evident that the fungi which they cultivate are not basi- 

 diomycetes but chromatogenic or wood-staining ascomycetes. Hedgcock 

 (1906) who has recently studied these fungi, describes a number of species 

 referable to the genera Ceraiostomella (wood-bluing), Graphium, Hormoden- 

 dron, Hormiscivm. (wood blackening and wood-browning), PeniciUium and 

 Fusariuvi (wood-reddening). Cultures of one of the species (Graphittm 

 ambrosligenim Hedge.) v\'ere made from material taken from the burrows 

 of ambrosia beetles in the wood of Piinis arizonica Eng. The mycelium 

 was seen to develop stromata with heads, and both primary and secondary 

 conidia, but the author records no observations on the relations of the 

 beetle to the fungus or the modifications produced in the food plant when in 

 the presence of the insect. From some investigations now in progress at 

 the Royal School of Forestry at Tharandt, Saxony, and communicated to 



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