86 



STATE HORTICULTURAL SOCIETY. 



•when fully developed possess six legs, while the mites and spiders have no 

 separation of head and thorax and in the case of the former there is no sep- 

 aration of thorax and abdomen, and when- full growth they possess eight legs, 

 as seen in the cut. Exceptions to this rule occur in the Phytopti which have 

 but four legs and in certain internal parasites that are entirely destitute of 

 less when fully grown. 



The young mites usually have six legs which might lead to their being con- 

 fused with insects, but the general shape of the body and legs enable us to 

 easily distinguish the one from the other. 



Among injurious species of mites none are more common than the Phytop- 

 tus, or gall-producing mites. The damage done by this fam- 

 ily is confined to the leaves and buds of plants and it seems 

 that the majority of our trees and shrubs are more or less af- 

 fected by them. 



About a year ago, Prof. Cook received several leaves of a 

 wild plum tree that were thickly set upon their upper surface 

 with reddish, teat-like projections. The seeker after knowl- 

 edge who sent the leaves desired to know what to do in case 

 the malady should be found spreading to tame plum trees in 

 the vicinity. He was advised to cut and burn the infested 

 tree which he wisely did. 



The owner of this tree might have searched never so care- 

 fully for the cause of the galls, and have been none the wiser 

 for his pains. On examining the inside of these excres- 

 cences with a compound microscope, little, whitish, elon- 

 gated, Phytoptus mites, from five to eight-thousandths of an 

 inch in length were found in large numbers in each little gall. 

 They were so small that if a large number were washed out 

 into a dish, they looked like minute particles of dust floating upon the surface 

 of the water. 



A representation of these galls, and the mite that produced them, may be 

 seen in Figs. 2 and 3. These mites have four plump, clumsy, six-jointed 

 legs near the front end of the body, and just back of them is a large, trans- 

 verse slit where the eggs are protected. A large number of 

 these little animals live and feed in a single gall where there is 

 plenty of room and food, and where they are shut away from 

 all disturbing influences from without. 



A gall almost identical with this, is the Trumpet grape gall, 

 with which the growers of the vine are probably familiar. 

 This gall, Fig. 4, is not produced by a mite, but by a Chalicid 

 fly, and differs from the mite galls by having the cavity within 

 entirely closed by a thickened wall of vegetable growth, while 

 all Phytoptus galls shave a small opening on the under surface of 

 the leaf, where the mites may go in and out at pleasure. All 

 galls produced by mites have this opening, Fig. 5. 



Fig. 3. 



Fig. 4. 



