RILEY — GENUS PRONUBA ; FERTILIZATION OF YUCCA. 59 



St. Louis, and which Dr. Engelmann takes to be T. puberula or 

 T. glauca. 



Dr. Engehnann has made some interesting observations on 

 the fertilization of Yucca,t and to him I am indebted for draw- 

 ing my attention to the fact that the plants of this genus must rely 

 on some insect or other for fertilization. The sagittate anthers 

 open a little earlier than does the perianth, and expel the pollen 

 grains, which, being glutinous, remain attached in different sized 

 lumps to the inside of the flower. The stigmatic tube contains 

 nectar, and is connected with the ovarian cells, and the pollen must 

 be introduced into the tube, but cannot be so inti^oduced without 

 artificial aid. 



There are several insects that frequent our Yuccas about flow- 

 ering-time. Some, doubtless, feast on the pollen, while others feed 

 either by gnawing into the young fruit or pumping the juices 

 therefrom ;* but the only insect which I have found actively en- 

 gaged in the pollenation is our little Tineid, which may be known, 

 in popular language, as the Yucca Moth. 



During the daytime, we may, by knowing what and where to 



facts, so far as known, strongly indicate that Pronuha is principally, if not solely, instru- 

 mental in bringing it about. Its seeds are infested with our Pronuba larva, though not to 

 the same extent as are those of the dehiscent species. It would be premature to speculate 

 until we have further facts; but it is not at all unlikely that the seeds of the fleshy pods are 

 less congenial to the larvae, and that a smaller percentage is produced from the e^gs con- 

 signed to such pods by the moth. In addition to the Pronuba larva in the seeds, the fruit of 

 7~. aloifolia nourishes a smaller white, apodous larva which is found in the pulp, sometimes 

 in considerable numbers. It may be traced from slight depressions on the outside, and shows 

 Hymenopterous affinities. It occasionally gnaws into the seed from the outside, but its leg- 

 less character will at once distinguish it from the larva of Pronuba, which will be described 

 further on. 



t See Bulletin of Torrey Botanical Club, vol. iii. No. 7. 



* I have taken the following insects from the flowers : Coleoptera — Anthonomus siff- 

 natus Sav, whose larva I have known to feed on certain Aphidan Hickory galls — Chauliog- 

 nathus Pennsylvanicus (DeGeer), and C. marginatus (Fabr.). Both these insects have the 

 maxillx peculiarly modified into slender, pilose, extensile setae or feelers, which doubtless 

 resemble in function die tongue of moths, and enable them to lap honey. I once thought 

 these might have something to do in the pollenation of the plant, and possibly they do in a 

 small degree ; but I could never find them near the stigma, and their sole object seemed to be 

 to feed upon the pollen, for which purpose their jaws are well suited. They are found on a va- 

 riety of pollen.bearing plants, such as Spiraa, Rubus, Solidago, etc .while as larvae they are 

 carnivorous, the first named being one of the principal enemies of those notorious fruit dep- 

 redators Conotrackelus nenuphar (Herbst) and Carpocapsa pomonella (Linn.) — Euryotnia 

 melancholica Gor. & Perch, a chafer very fond of eating into the flowers and fruit of a variety 

 of plants. Heteroptera — Lygus robiniee Uhler — Orthotylus discoidalis Uhler — Cylloco- 

 ■ ris scutellatus Uhlec— Theognis phyllopus Uhler (= albicinctus Say). The last is notably 

 found on Yuccas, but the others more commonly on other plants, and they all derive nour- 

 ishment by puncturing and sucking, their punctures causing little rusty specks on the fruit. 



