11 



All the growing parts of the fungus are extremely succulent and 

 tender. The conidia especially are always pellucid, and glisten like 

 pearls or like drops of dew. When the plant Lb in active growth, conidia 

 are produced in the greatest abundance, growing sometimes Binglj 

 the end of short straight stems, as in figs. 20 and 23, sometimes in 

 grape-like clusters among interlacing branches, as seen in fig. 4. At 

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

 coating of hoarfrost. The young larva- nip off these tender tipe 

 calves crop the heads of clover, but the older larva- and the adult 

 ties eat the whole structure down to the base, from which it soon springs 

 up afresh, appearing in little white tessellations upon the walls. 



The growth of ambrosia may mi fact be compared to asparagus, which 

 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 over- 

 whelmed 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 overproduction of the ambrosia. It accumulates, 

 ripens, and discharges its spores, choking the galleries and often suffo- 

 cating the remaining inhabitants in their own food material. The same 

 results may sometimes be brought about by closing the outlets ofrttie 

 galleries through the bark, or by spraying into them kerosene or some 

 other noxious liquid. The inmates of the colony are thereby thrown 

 into a panic, the beetles rush hither and thither through the galleries. 

 trampling upon and crushing young larva- and eggs, breaking down the 

 delicate lining of ambrosia on the walls of the brood chambers and pud- 

 dling it into a kind of slush, which is pushed along and accumulated 

 in the passage ways, completely stopping them in places. The break- 

 ing 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 o( 

 mycelium, in which the living insects are suffocated and destroyed. 



The ambrosia does not make its appearance by accident or at random 

 in the galleries of the beetles. Its origin is entirely under the control 

 of the insect. It is started by the mother beetle upon a carefully 

 packed bed or layer of chips, sometimes near the entrance, in the bark, 

 but generally at the end of a branch gallery in the wood. In some 

 species the ambrosia is grown only in certain brood chambers of pecu- 

 liar construction. In others it is propagated in beds, near the cradles 

 of the larva-. The excrement of the larva' is used in some and proba- 

 bly in all the species to form new beds or layers for the propagation oi' 

 the fungus. 



