48 Journal of the Mitchell Society [December 



no more comniont than the rising of the sun. Yet the elaborate floral 

 devices, the presence of artfully concealed nectaries on the one hand 

 and the presence of long tongues and pollen baskets among the insects 

 show an evolution that must have been carried on for untold ages. 

 And how dependent one group is on the other and any failure of the 

 one group must necessarily mean the extinction of the other. I won- 

 der how many such cases of sad wrecks we might find if we could re- 

 construct the past geological ages. 



The highest form of interdependence is found perhaps in the case 

 of the Yucca and the Yucca moth. 



"The flowers of the species of Yucca are absolutely incapable of 

 self-or-wind-pollination, and the stigma is so situated that no ordinary 

 insect visitor can reach it in a casual search for food. In some locali- 

 ties, it was observed that the common Yucca never produced seed and 

 that wherever seed was produced, almost every pod was infested by a 

 little caterpillar that destroyed a greater or less percentage of the seeds. 

 The parent of this caterpillar is a small Avhite moth, the Yucca moth, 

 in which the mouth-parts are curiously modified and utterly unlike 

 those of any other moth species that we know. At the sides of the 

 ordinary tongue there are developed a pair of flexible processes set 

 with little pegs and spines, and capable of being coiled like the tongue 

 itself. When the female, which alone has these processes, is ready to 

 lay an egg she enters a Yucca blossom, gathers a little mass of pollen, 

 rolls it into a ball, carries it by means of the processes to the pistil, and 

 rams it down so as to bring it into direct contact with the receptive 

 surface. Not until this has been completed does she turn and then 

 into the ovary or embryo seed pod, she forces an egg by means of a 

 slender, sharp-pointed ovipositor. She is now ready to repeat the 

 process on another flower and she does repeat it until her stock of eggs 

 is exhausted. Here we have a deliberate pollination preceding oviposi- 

 tion, as if the insect knew that it would be useless to lay an egg until 

 the possibility of development in the seed pod was assured. 



"This peculiarity, though confined so far as we know to the genus 

 Pronuba, is not confined to one species only. There are a number of 

 Yuccas in the country, including the giant or tree Yuccas of the south- 

 west, and for every species of Yucca there is a species of Pronuba. 

 Surely a most wonderful adaptation of insect and plant, neither of 

 which can exist without the other. 



"And yet, while the adaptation is not so specific, nor the evidence 

 of design so apparent, the dependence of red clover upon long-tongued 



