28 TRANS. ST. LOUIS ACAD, SCIENCE. 



that of gathering the pollen. The three stigmas, emarginate or bi- 

 lobed at the summit, are more or less united, and form a tube ; 

 they are generally erect, but in some species, especially in the true 

 T.Jilamentosa, they are at last patulous and even recurved. The 

 inside of the stigmatic tube, somewhat triangular in the transverse 

 section, with three pairs of tiny prominent ridges, corresponding 

 to the commissures of the carpels, is coated with much smaller 

 and less elevated, truly stigmatic cells, which exude the stigmatic 

 liquor, under the influence of which alone the pollen can develope. 

 The tube terminates near the upper ends of the three ovarian cells* 

 and seems to communicate directly with them. 



Hesperoyucca has an obovate ovary of a similar structure, 

 crowned by a shorter or longer, sometimes filiform style, bearing a 

 very peculiar, large, hood-shaped, trilobed stigma, beset with long 

 filiform papillae. 



The color of the stigma is usually of a pearly white, while the 

 ovary is dull or greenish-white ; only in T. angustifolia, I find 

 the stigma bright green. 



FECUNDATION. 



The fecundation of the Yucca flower, as has been stated in the 

 introduction, is very uncertain, and evidently depends on con- 

 tingencies not always attainable, so that very often in its native 

 condition, and almost always in cultivation in Europe, these plants 

 remain sterile. The flower can only be fertilized by the intro- 

 duction of the pollen into the stigmatic tube ; this at least in the 

 capsule-bearing Yuccas, which alone I have been able to examine 

 in the growing state, is accomplished almost always by a noctur- 

 nal insect, the Promiba yuccasella (thus named by Mr. Riley 

 and described in the next paper). Even where we are unable to 

 observe the moth itself, its traces are manifest in the presence of 

 its offspring, the larvae, feeding on the maturing seeds, tunneling 

 their rows and finally emerging through a perforation of the cap- 

 sule. Wherever, therefore, we find such perforated capsules, or 

 merely the remaining annular rim of seeds, we know that Pronuba 

 has been at work. The capsules and seeds of the Californian 

 Hesperoyticca also show the unmistakable traces of this or a 

 similar insect. On an average in our gardens, as well as in the 

 fields of the coast of South Carolina, about two-thirds of the cap- 

 sules and their seeds bear the marks of these larvae. 



