i86 THE POPULAR SCIENCE MONTHLY. 



habitually fertilizes it is even closer and more lasting than in any of 

 the instances we have yet considered. Everybody knows those large 

 and handsome tropical lilies, the yuccas, with their tall, clustered heads 

 of big white blossoms. Well, Professor Riley, the great American 

 entomologist, has shown that the yuccas are entirely run (to use a 

 favorite expression of his countrymen) by a comparatively small and 

 inconspicuous moth, solely for its own benefit : and so completely is 

 this the case, that the yucca can't manage to exist at all without its 

 little winged intermediary. Professor Riley has, therefore, playfully 

 named the little insect Pronuba yiiccasella ; freely translated, the yuc- 

 ca's bridesmaid. The moth bores the young capsule of the flower in 

 several places, lays an egg in each hole, and then carefully collects pol- 

 len, with which it fertilizes the blossom, of set purpose, thus deliber- 

 ately producing a store of food for its own future larvae. The eggs 

 hatch inside the capsule, and the young grubs eat part of the seeds, at 

 the same time prudently leaving enough for the continuation of the 

 yucca family in the future. As soon as the grabs are full-grown, they 

 bore a hole again through the capsule, lower themselves by a thread 

 to the ground, and there spin a cocoon which lies buried in the earth 

 all through the autumn and winter. But in the succeeding summer, 

 just fourteen days before the yuccas begin to flower, the grubs in their 

 cocoons pass into the chrysalis stage ; and, by the time the yuccas are 

 in full blossom, they issue forth as perfect moths, and once more com- 

 mence the fertilization of their chosen food-plant, and the laying of 

 their own eggs. So singular an instance of mutual accommodation 

 between flower and insect is rare indeed in this usually greedy and 

 self-regarding world. 



The extremely odd, inside-out, topsy-turvy flowers of the fig owe 

 their fertilization, however, to a still more extraordinary and compli- 

 cated cross-relationship. Hardly anybody (except a botanist) has ever 

 seen a fig-flower, because it grows inside the stalk, instead of outside, 

 and so can only be observed by cutting it open lengthwise. The fig, 

 in its early youth, in fact, consists of a hollow branch on whose inner 

 surface a number of very small flowers cluster together ; and, when 

 they are ripe for fertilization, the eye or hole at the top opens to ad- 

 mit the insect visitor. This visitor is the fig-wasp, who comes, not 

 from other cultivated fig-trees, but from a wild tree called the capri- 

 fico. On this tree the mother wasps first lay their eggs in the inedi- 

 ble figs, which thereupon swell out into galls, and become the nurses 

 of the young wasp-grubs. When the wasps are mature, they eat their 

 way out of the wild fig where they were born, and set forth to lay 

 their own eggs in turn, either on a brother caprifico or on its sister, a 

 true fig-tree. Those wasps which enter the wild figs of a caprifico 

 succeed in carrying out their maternal purpose, and lay their eggs on 

 the right spot for more grubs to be duly developed. But those which 

 happen to go into a true fig merely fertilize the flowers without laying 



