84 



you touch it, the chances are it falls to pieces, being a mere dry 

 shell, the interior of which has been completely eaten out. If you 

 have seen this phenomenon, you wlH probably have also noticed 

 — (though perhaps without attaching much importance to the fact) 

 —that the fly was surrounded by a filmy cloud which covered the 

 glass, and extended over it for an inch or two on every side. But 

 in point of fact this dehcate white mass is the real " causa doloris," 

 " the head and front of the ofiending "—it is a plant, a fungus, or 

 mould. Now when a spore or seed of this mould comes in contact 

 with a living fly, it forthwith sends out a delicate process which 

 bores its way through the skin into the interior cavities of the body, 

 just as does the mistletoe into the heart of the hawthorn or apple. 

 Here it gives rise to minute corpuscles which, floating in the juices 

 of the insect, multiply and lengthen into new filaments at the 

 expense of the fly's substance, and ultimately are the cause of its 

 decease. "^ No sooner does death ensue, than the filaments issue 

 into the world through the openings between the segments of the 

 animal's abdomen, spreading on every side, each tiny thread being 

 the fertile bearer of innumerable spores or seeds, destined to work 

 like ruin among new generations of flies. 



A second species of the same plant has been detected on the 

 common gnat. Another of these moulds, Botrytis hassiana — (so 

 named after its first investigator, Dr. A. Bassi) — attacks the silk- 

 worms of Italy and Southern France, producing a disease caUed 

 Muscardine, which has for some years caused great apprehension 

 among silk-growers. Its true character, in spite of the incessant 

 and careful observations that have been brought to bear upon it, 

 has even yet scarcely been made out with any certainty. It is not 

 even ascertained whether it is identical genericaUy with the fungus 

 which attacks the flies. 



It is probable, however, that both of them are merely incipient 

 states of some more highly organised plant, t Be this as it may, of 

 its destructive powers there is no doubt, more especially during the 

 caterpillar stage of the insect's existence ; though the chrysalis is 

 sometimes affected in the cocoon. The germs of the fungus once 

 introduced spread through the fatty matter stored up beneath the 

 skin, propagating themselves with extraordinary celerity, and sooner 

 or later causing the death of the victim. It is only when life is 

 extinct, that the plant shows itself externally, throwing up spore- 

 bearing stems. These quickly ripen, and are the means of scattering 

 the disease far and wide, for it has been ascertained that the mere 

 contact of a spore -with the insect's skin, without actual inoculation, 

 is quite suflicient to ensure its growth. Where the disease has once 

 established itself, all remedial measures appear to be hopeless, and 

 the proprietor usually turns his attention to procuring a new stock 

 from an uninfected source. 



Cordiceps is the name of a fungus consisting, in its perfect form, 

 of a stem varying in length from a few lines to four or six inches, 

 and terminating in a pointed or club-shaped head of spores. 



It is the same fungus to which I drew your attention a short time 

 ago, when making some remarks on ergot in rye-gi-ass. Ergot is, in 



*Huxley . (Opening address, British Association, 1870. ) 

 tBerkely. (Introduction to Crytogamic Botany.) 



