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



"Two principal types exist among the varied forms of these minute 

 fungi: (1) Those with erect stems, having at the termination of the stems, 

 or their branches swollen cells (conidia) [PI. LII, Fig. 65]. (2) Those 

 which form tangled chains of cells resembling the piled-up beads of a broken 

 necklace. The erect or stylate forms are found among those species of the 

 beetles whose larvje live free in the galleries (Platypus and Xylehorus). The 

 bead-like or moniliform kinds appear to be peculiar to the species whose 

 larvae are reared in separate cells or cradles (Corthylus, Monarthrum, etc.). 



"All the growing parts of the fungus are extremely succulent and tender. 

 The conidia especially are always pellucid, and glisten like drops of clew. 

 When the plant is in active growth, conidia are produced in the greatest 

 abundance, growing sometimes singly, at the end of short straight stems, 

 sometimes in grape-like clusters among interlacing branches. x\t such 

 periods the fungus appears upon the walls of the galleries like a coating 

 of hoarfrost. The young larvse nip off these tender tips as calves crop the 

 heads of clover, but the older larvje and the adult beetles eat the whole struc- 

 ture down to the base, from which it soon springs up afresh, appearing in 

 little white tesselations upon the walls. 



"The growth of ambrosia may in fact be compared to asparagus, v\'hich 

 remains succulent and edible only when continually cropped, but if allowed 

 to go to seed is no longer useful as food. In like manner the ambrosia fungus 

 must be constantly kept in fresh growth, otherwise it ripens; its cells burst 

 and discharge the protoplasmic granules which they contain in myriads, 

 and the entire plant disappears as if overwhelmed by a ferment. 



"Various disturbances of the conditions necessary to its growth are apt 

 to promote the ripening of the fungus, and this is a danger to which every 

 colony of ambrosia beetles is exposed. If through any casualty the natural 

 increase of a populous colony is checked, there results at once an overpro- 

 duction of the ambrosia. It accumulates, ripens, and discharges its spores, 

 choking the galleries and often suffocating the remaining inhabitants in 

 their own food material. The same results may sometimes be brought 

 about by closing the outlets of the galleries through the bark, or by spraying 

 into them kerosene or some other noxious liquid. The inmates of the 

 colony are thereby throwm into a panic, the beetles rush hither and thither 

 through the galleries, trampling upon and crushing young larvje and eggs, 

 breaking down the delicate lining of ambrosia on the walls of the brood 

 chambers and puddling it into a kind of a slush, which is pushed along and 

 accumulated in the passage ways, completely stopping them in places. 

 The breaking down of the food fungus follows and in a few days the galleries 

 are filled with a paste-like mass of granules or spores, or with threads of 

 mycelium, in Avhich the living insects are suffocated and destroved. 



