50 J. PERCY BAUMBERGER 



The consideration of main interest in the present paper is the 

 pecuUar relation of substratum, microorganism, and insect which 

 again finds an example in the food of this animal. It is is well 

 known that molds contain enzymes capable of dissolving cellu- 

 lose and hemicellulose, i.e., celluloses and cytases, which enable 

 them to extend hyphae throughout the woody tissue of trees, 

 etc., thus extracting all the nutritional substances. The nitrog- 

 enous natter is largely stored in the form of protein in the spores 

 of the fungus, whereas the excess of carbohydrates may be 

 excreted in the sticky drops of the sporophores. The insect feed- 

 ing on the fungus, the wall of which it can dissolve, derives the 

 benefit of the enzyme activities of the mold. If a section is made 

 through larvae which have been feeding in the wood, it is seen 

 that the great quantities of wood that pass through the digestive 

 tract remain unchanged in structure. On closer examination 

 fungous growths of an exobasidiomycete can be seen in the tissue 

 cells (fig. 17). These fungi are dissolved out by the insect diges- 

 tive enzymes and serve as food. The wood eaten by Sciarid 

 larvae is therefore merely the substratum in which the fungous 

 food material is embedded. This type of relationship is quite 

 common among 'wood-eating' insects and is quite comparable 

 to the symbiosis of Drosophila and yeast. 



h. Experiments with a mycetophagoiis mite living in decaying 

 wood. A mite of the genus Tyroglyphus (determination by Mr. 

 N. Banks) was also found 'on decayed mountain-ash twigs and 

 bred upon bran agar hke the Dipterous larvae described above. 

 Five mites added to the tube climbed about on the thick growth 

 of fungus, apparently eating the spores in the muclaginous 

 sporangia. As the mites rapidly multiplied the growth of the 

 molds was checked and they were cleaned off the surface till only 

 a few blisters or pustules of Fusaria remained. The mites could 

 be seen to feed in large numbers at the edge of these pustules 

 which served as food for two months allowing the mites to in- 

 crease enormously in size and number. Many of this same genus 

 of mites are known to feed on cheese, ham (on which powdery 

 molds grow), and dry molds of various kinds, and manure, de- 

 caying fungi, and vegetable refuse are always inhabited by mites 



