THE BUST MITE. 117 



to twelve feet per hour. It is therefore not surprising to 

 find them changing their position frequently; disappear- 

 ing suddenly from one portion of the tree, and appearing 

 as suddenly in great numbers upon another and distant 

 part of the same tree. 



It is not to be understood that the mites show any con- 

 cert of action in moving their colonies, or that they are in 

 any other sense gregarious than that they are usually found 

 very thickly scattered over those parts of an infested plant 

 which offer favorable conditions for their support. Thus 

 the new growth of many orange trees becomes occupied or 

 infested by them as rapidly as the leaves fully mature, and 

 the number upon a single leaf may be estimated by many 

 thousands. 



Numerical Abundance. The following examinations, made 

 in January, will give an idea of the extent of the brood 

 during the coldest parts of the Florida winter : 



From a large number of leaves in late autumn growth 

 one was selected which showed an even distribution of 

 mites upon its surface. An area of one square inch was 

 accurately marked out with a needle, and subdivided into 

 sixteen equal squares. The number of mites and their 

 eggs upon four of the small squares taken at random was 

 counted, and found to aggregate 1,142.* This gives for 

 the square inch under observation 4,568 mites. The leaf 

 was then cut into squares and triangles, and was found to 

 cover fifteen square inches upon a sheet of paper. 



On the supposition that the experimental square inch 

 gives a fair average, the number of mites upon the upper 

 surface of this leaf was 68,520. Certain portions, not 

 exceeding one quarter of the whole, were, however, more 



*The number of eggs exceeded that of the mites, a phenomenon not 

 often observed, and which may be attributed to the unusually cold and un- 

 favorable weather at the time of the examination and for several weeks pre- 



