Dec. 1910.| BOTANICAL SOCIETY OF EDINBURGH 13] 
Even in this country it is unusual to find either “red 
spider” or “ Phytoptus” on the same leaf as the benignant 
mites. I have never myself seen them together, and very 
seldom seen aphides accompanying the true mites. 
Certain observations which have been made on the 
habits of the benignant mites are of great importance. 
Their mouths are not adapted for sucking the sap of 
plants, but for chewing or biting (Aurivillius (15)). Lund- 
strom himself saw fungus spores between the mouth parts 
of living acarids. Spores and fragments of fungus hyphee 
have been found in their shelters. Dr. Aurelio de 
Gasparis caught Tydews foliorwm in the act of piercing 
an insect’s ege. 
According to Banks (16), Tydews gloveri eats the eggs 
and young of scale insects, and both Rhyncholophus and 
Cheyletus are also said to prey on scale insects. Cheyletus 
also eats the eggs of a cicada, and certain Gamarid mites 
live on minute plants, bacteria, small fungi, ete. 
These observations seem almost to prove the truth of 
Lundstrom’s suggestion. It would be interesting to try if 
these mites could not be utilised to keep down “mussel 
scale” and similar pests in greenhouses. 
These mites, therefore, may be regarded as an active 
and numerous police, keeping in check all sorts of fungus 
and insect pests which might otherwise do serious harm. 
But there is another possibility which, to my mind, is of 
even more importance. 
The atmosphere is, in its lower layers, crowded with 
enormous quantities of motes or dust-particles. They are 
of the most diverse origin. Of the inorganic dust-particles 
some did not belong to our earth originally, but formed 
part of a falling star or perhaps a comet’s tail. Other 
particles have been thrown out in volcanic eruptions. The 
dust from Krakatoa, for instance, is said to have been 
reflected out and back again, and to have passed right 
round the world three or four times. 
Fine dust from the Sahara and other deserts probably 
travels great distances. I have seen quantities of it on a 
steamers deck quite a long way from shore. Mr. John 
Aitken (17), in one of his classical papers on this subject, 
describes how dust-particles from the densely inhabited 
