THEIR RELATION TO PLANTS 49 



its power to maintain life and reproduce its kind; which 

 be it noted, is quite a different matter from an injury 

 which will make the plant unprofitable to the farmer 

 or fruit-grower. 



Scale insects are close alhes of plant lice in many 

 ways and yet totally different in "many others. The 

 popular name is derived from the fact that most of the 

 species have the appearance of a fragment or scale of 

 tissue plastered upon or against the ' bark or foliage 

 of the plant attacked. And so we have soft scales and 

 armored scales, which differ radically from each other. 

 In the soft scales, so named because the outer covering 

 is usually waxy in texture, the outer covering or scale 

 is part of the insect itself, not separable from it in any 

 way, and the term, scale insect, is strictly correct. In 

 the armored scales, on the other hand, the scale or 

 covering mass is tougher, more parchment-like, and 

 forms no part of the insect, although produced or ex- 

 creted by it. It is possible, therefore, to lift the scale 

 without in any way interfering with the creature be- 

 neath it; the covering being formed in part by the 

 cast skin of the insect and in part by a fibrous excre- 

 tion from special glands. 



Scale insects, like plant lice, are capable of enormous 

 feats in the reproductive line, one thousand million de- 

 scendants for a single pair, during a single season, 

 having been figured out for one of the species! Thus, 

 given a scale introduced without natural checks into 

 a region where conditions favor it, and the effect upon 

 its host-plant can be readily imagined. The practical 

 experience of the Pacific Coast with the cottony cushion 

 scale on citrus fruits, and of the Atlantic Coast with 

 the San Jose scale, are recent instances that illustrate 

 the destructive powders of scales; the first a soft, the 

 latter an armored form. 

 4 



