Dust and its Importance to Plant Life. 15 



number on different leaves of the same plant. Most of the plants 

 were examined in September and October. 



Out of the 220 plants examined (excluding ferns), I could not 

 find any definite arrangements for collecting or utilising dust in 

 18 cases. 



Now the list, in no way specially selected, was most miscel- 

 laneous, and consisted just of whatever plants I could manage to 

 examine, and, except that I intentionally excluded Coniferse, it 

 was a " random " selection. 



Of this miscellaneous series, then, from 91 to 92 per cent, 

 showed distinct arrangements for making use of the dust. 



As regards mites, I found none upon plants grown in the 

 greenhouse (owing to the precautions taken against Red Spider). 

 Deducting the 26 greenhouse plants, there were 194 plants 

 examined, and mites were found upon 112, so that about 57 per 

 cent, of these plants were inhabited by them. 



This seems sufificient to show that mites are far more common 

 than is usually supposed. 



From my observations I am convinced that they are very 

 abundant; they occur more frequently on trees and shrubs than 

 on herbaceous plants, but are also found, though rarely, on mono- 

 cotyledons. 



As regards special mite-shelters or acarodomatia, they are 

 by no means rare even in a climate like our own. I have found 

 no less than 35 plants on which one can find special hollows or 

 crevices mhabited by mites, and which appeared to me to be both 

 adapted for them and, at any rate in some respects, altered bv 

 them. Such mite shelters were seen on one monocotyledon, on 

 tour of the smaller herbaceous plants, but e.specially on tall herbs 

 shrubs, and trees. Hitherto it has been supposed that acaro- 

 domatia are never found except on dicotyledonous shrubs and 

 trees But it is very difficult to define exactly what is meant bv 

 acarodomatia, and it is quite probable that most botanists would 

 not admit that several of the mite shelters which I discovered are 

 real acarodomatia. 



dhcltr Jf°^' ^"angements for utilising dust which I have 

 discovered during this examination are very difficult to classify 



Ihose plants which are covered with a glaucous bluish-white 

 bloom are usually unwettable or " rain-shy. ' ' Amongst the most 

 interesting are Bocconia, Asparagus, Hypericum perforatum, and 



