THE ACARIXA OR MITES. 



135 



Fig. 279.— Eriopliyes gossypii: Ante- 

 rior part of body. (Author's illas- 

 tration.) 



Fig. 280.— Dimple gall. (Original.) 



Therefore he believed these mites to be adults and named them Phytoptus. A tew 

 years later Scheuten examined the pear-leaf blister, found the mites, and decided 

 that they were immature forms and that the full- 

 grown creature was an eight-legged mite that he 

 found associated with them. This supposed adult he 

 figured, and it proves to be a parasitid, which was 

 doubtless feeding on the Eriophyes. Since then many 

 observers have examined these mites and confirmed 

 Dujardin's conclusion that they are adult and consti- 

 tute a separate group of acari. 



The deformations produced by mites on plants have 

 been called "aairo-cecidii." Nearly all such defor- 

 mations are produced by members of this family. 

 The relation of the mite to the gall or erineum is not 

 fully known. An erineum is practically a dense 

 mass of deformed hairs. These hairs are usually 

 thickened and twisted and the whole mass is of an 

 even height. The mites live among these deformed 

 hairs, sucking the juices of the leaf. As the juice 

 becomes exhausted the erineum becomes reddish or rusty brown in color and is a 

 very prominent object. At this stage, when the erineimi is most easily noticed, one 



is apt to find few if any mites as they have left for 

 fresh pastures. The galls may be on either surface 

 of the leaf, though commonly above. The form is 

 quite characteristic of the species, though there is 

 usually some variation. These galls always have an 

 opening tlirough which the mites can pass. This character will distinguish these 

 galls from those of Diptera and Hymenoptera, but not from homopterous galls. The 

 opening is often very small and concealed by tufts of hairs. 

 Within the gall is often partly filled up with folds and projec- 

 tions and sometimes with hairs. In color the gall is at first 

 like the leaf, but gradually turns yellow or reddish and then 

 brown or black. Sometimes the gall covers a great deal of space 

 but does not swell up much, being in appearance much like a 

 blister. Galls are formed while the leaf is growing rapidly. 

 It is supposed that the puncture of the plant cells by the mite 

 induces an increased flow of sap in that direction, which causes 

 the spot to grow faster than the surface around it, so that tliis spot must swell up in 

 the form of a gall. Tiiis does not accoimt for the diversity of form of the galls hot 

 explain why each gall is characteristic of the mite that made it. 

 Some species of Eriophyidae live in plant buds, and their feed- 

 ing prevents the opening of the bud, which after a time dries 

 up and dies. With other species the buds swell to a great size, 

 but never open. Other mites produce a curling or rolling of 

 the edge of the leaf or a slight folding of the surface. Some 

 live on the surface of fruits, as the orange rust mite. A few 

 species produce g*alls or excrescences on twigs, especially near 

 the base of the terminal buds. 



The diseased condition produced by these mites has been 

 termed phytoptose or erinose. Sometimes the stems are de- 

 formed into long, slender filaments, making a broom-shaped 

 object, commonly called "witch's broom" in England. One 

 occurs in this country on the hackberry. It is probable that the sliape of the trail is 

 dependent upon a secretion of the mite, since in some cases two species of mites occur 



Fig. 281.— Capsule gall. 

 (Original.) 



Fig. 282.— Pouch gall. 

 (Original.) 



