570 TRANS. ST. LOUIS ACAD. SCIENCE. 



force in what he savs against the general rule laid down by Baird 

 and Packard. 



White moths are naturally attracted to white flowers, and it 

 is rash to assume, without careful examination, that all white 

 moths found in Yucca flowers are Pronuba. 



An interesting fact connected with Yucca pollination came to 

 my notice in the summer of 1S76. I have elsewhere shown that 

 the Pronuba larva, as it lies in the cocoon underground, is not 

 susceptible to the forcing influences that hasten the development 

 of most other insects. The moths usually issue in St. Louis too 

 late to pollinize the flowers of Yucca angustifolia. This species 

 blooms from two to three weeks earlier than Y. filamentosa. which, 

 with its varieties, is most commonly cultivated. As a consequence, 

 the former very rarely produces seed. One of the rare occasions 

 on which it did so was in the year stated, in the garden of Dr. 

 Engelmann. All the early flowers at the base of the raceme fell 

 infertile, but a few of the very latest at the apex were fructified. 

 and, as the subsequent discovery of the Pronuba larva in the cap- 

 sules proved, they had been duly visited by the moth. 



Since the publication (pp. 208-210, this vol.) of the article 

 " On the Oviposition of the Yucca-moth," the experience of three 

 summers has confirmed everything there said both as to the mode 

 of oviposition and pollination, and as to the remarkable fact that 

 Pronuba is the sole pollinizer of our Yuccas. This reiteration of 

 the facts there recorded will scarcely seem necessary to those who 

 have carefully perused what I have written. But one writer, Prof. 

 P. C. Zeller, in Stettin. Prussia, has seen fit to doubt the accuracy 

 of the observations ; while a second. Mr. J. Boll, of Dallas, Texas, 

 has attempted to refute my conclusions, in an article in the Ento- 

 mologische Zeitung (1876, pp. 401-5), published at Stettin. To this 

 article I wish, briefly, to reply ; for I do not deem it altogether a 

 waste of time, in a mattter so interesting, to notice even that which 

 is palpably superficial and erroneous. 



Prof. Zeller, as already shown in these Transactions (p. 325, 

 note), considers the $ maxillary tentacles "not available" for pur- 

 poses of pollination, notwithstanding I had shown so clearly that 

 they were. "The strong tongue seems to me alone available 

 therefor," he writes, and then vouchsafes the opinion that "other 

 observers will be necessary to entirely clear up the curious cir- 



