14 Dust and its Importance to Plant Life. 



have special shelters inhabited by colonies of mites are not injured 

 by leaf parasites.* 



Lundstrom goes so far as to suggest that there is a sort of 

 warfare between the benevolent mites and those, like " Red 

 Spider," which are leafsuckers. If this is correct, it is curiously 

 similar to what is known to be true with regard to ants. For the 

 worst enemies of the Leaf-cutting or " Parasol ' ' ants are the fierce 

 soldier-ants, which are supplied with board and lodging by 

 Cecropia and other myrmecophilous plants. 



I have not been able to come to any conclusions upon this 

 point, for I am not a good enough entomologist to be able to see 

 how mites make war. But it is my impression that it is exceed- 

 ingly unusual to find the benevolent mites and Red Spider on the 

 same leaf. But besides being possibly guardians and a sort of 

 fungus police, mites may be of great importance in another 

 respect. Their excrement has been found to be an excellent 

 material for the growth of fungi, and must surely be of great 

 fertilising value, t If they are very common on plants and live 

 upon the germs and spores of all sorts of fungi, on lichen soredia 

 and algal cells, of which quantities are found in the dust on leaves, 

 then, especially as bacteria are also apparently always present, 

 plants will be able to utilise in a very perfect way all the valuable 

 matter that is supplied by atmospheric dust. 



I thought it would be interesting to find out if arrangements 

 for utilising dust were at all common on ordinary plants. Unless 

 mites are also commonly found upon leaves their influence cannot 

 be of much importance. 



I found that mites are very common indeed on plants of all 

 kinds. 



The so-called " Acarodomatia " or mite shelters are usually 

 placed at the vein-forkings on the under side of the leaves. They 

 are really small caverns or pouches in the tissue, and are sur- 

 rounded by a rich growth of peculiar hairs, which form a sort of 

 floor, or pallisade, -protecting the entrance. The anatomical 

 features of these mite shelters are very remarkable, and they are 

 quite unmistakeable and easily distinguished. They are only 

 well developed when inhabited by mites, and vary considerably in 



* Lundstrom, Malme. t Jungner. 



