THEIR RELATION TO PLANTS 43 



They are insignificant as individuals; but dangerous 

 in hosts: and hosts grow out of individuals in an in- 

 credibly short time, owing to their fecundity. Given 

 a few eggs on the tip of an apple twig in winter, they 

 hatch into young lice as soon as the leaf-buds open 

 and, in a week or ten days, depending upon weather 

 conditions, these begin to bear living young. All the 

 specimens hatching from the winter eggs are parthen- 

 ogenetic females; i.e., females which do not require 

 to be mated with a male before reproducing their kind; 

 and, when once reproduction begins, it is in the nature 

 of a continuous performance; four, six, eight or more 

 young being produced in a day and for several days in 

 succession. Long before this stem-mother has reached 

 her limit of increase, the first-born daughters, partheno- 

 genetic like herself, have in turn begun the task of 

 multiplication so that, by the time the leaves are fully 

 formed, the surfaces are covered by plant lice, and in- 

 stead of unfolding and reaching full size, they are 

 curled, twisted and crippled, forming an unsightly 

 mass instead of a beautifully unfolded cluster or tuft. 

 And now we are apt to get a secondary effect due to 

 a peculiarity in feeding. Not content with absorbing 

 only enough to sustain life and to reproduce, the insects 

 gorge continuously and, when incapable of containing 

 more, they eject through the anus a stream of a clear 

 sweetish liquid, known as honey -dew. It was cur- 

 rently believed that the two tube-like structures near 

 the end of the abdomen were the chief organs through 

 which this honey-dew is excreted and they are there- 

 fore popularly known as "honey-tubes": more technic- 

 ally they are termed cornicles, which conveys no opinion 

 as to their function. This honey-dew drops upon the 

 leaves below, often in such abundance as to form a 

 complete coating and that, in turn, is an excellent 



