MISSOURI BOTANICAL GARDEN BULLETIN 85 
the Yucca and its associated insect was Dr. George Engel- 
mann, fittingly styled the pioneer botanist of the West, a 
resident of St. Louis and with whom the early history and 
foundation of the Missouri Botanical Garden is so closely 
associated. Dr. Engelmann’s interest in the Yuecas began 
over fifty years ago, a time when but four species were 
generally recognized. Explorers of the West and Southwest 
sent or brought to him many specimens of the genus—their 
leaves, flowers and fruits. These, however, did not clearly 
harmonize with such knowledge of the group as had pre- 
viously been obtained and the greatest confusion existed as 
to the plants. The largest herbaria were notably poor in 
material, especially of fruits and seeds. Dr. Engelmann, 
in his studies and explorations in Europe, was struck with 
the fact that Yuccas rarely ever fruited in that country. 
He already knew that specimens and reports from collectors 
on the Atlantic coast and the western plains, where various 
species were indigenous, showed that both fruits and ripe 
seeds were preduced abundantly. The scientist’s question, 
why? appealed to him and he set about to solve the problem. 
- From his knowledge of the processes of pollination he sus- 
pected this work was carried on by some insect native to 
the habitat of the Yuccas, but as yet not introduced into 
Europe with the plants. Careful observations on the flowers 
of Yuccas growing beneath the window at his St. Louis 
home were soon rewarded with success. All circumstantial 
evidence pointed to a tiny white moth as the object of his 
search; a conclusion further substantiated by the discovery 
of the moth in the flowers of Yuccas growing in other and 
more remote parts of the city. Since Dr. Engelmann was 
a botanist, he was interested chiefly in the plant side of the 
subject and at this point he turned the investigation of the 
insect over to Dr. C. V. Riley, then the State Entomologist 
of Missouri. Together they observed and worked till the 
beautiful story of two life-histories was disclosed—one, of 
the plant; the other, of the insect. Dr. Riley’s studies 
revealed to him that the moth was so highly specialized, 
more noticeable in the mouth parts and the egg-laying de- 
vice, as to be entirely different and distinct from any other 
moth of its near kindred that had previously been described. 
Thereupon he gave to it the technical name of Pronuba 
yuccasella, the “Yucca Pronuba,” or “Pronuba Moth.” 
_ The Yucca flower, as has been stated, is almost closed 
in the daytime and but few insects can enter it. Neither 
does it produce nectar—the chief attraction to insects that 
