284 NOTES ON THE GENUS YUCCA. 
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 develop. The tube terminates 
near the upper ends of the three ovarian cells, and does communicate directly with them. 
esperoyucca has an obovate ovary of a similar structure, crowned by a shorter or longer, some- 
times filiform style, bearing a very peculiar, large, hood-shaped, trilobed stigma, beset with long 
filiform papille. 
The color of the stigma is usually of a pearly white, while the ovary is dull or greenish-white ; 
only in Y. 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 contingencies not always attainable; so that very often in its native con- 
dition, and almost always in cultivation in Europe, these plants remain sterile. The flower can only 
be fertilized by the introduction 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 nocturnal insect, the Pronuba 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 larve, feeding on the maturing seeds, tunnelling their rows and finally 
emerging through a perforation of the capsule. Wherever, therefore, we find such perforated cap- 
sules, or merely the remaining annular rim of seeds, we know that Pronuba has been at work. The 
capsules and seeds of the Californian Hesperoyucca 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 capsules and their seeds bear the marks of these larvee. 
Of the baccate Yuccas, Y. gloriosa and its allies seem to bear fruit very rarely,as neither [29] 
my correspondents nor I myself have thus far ever been able to obtain one; Y. Zreculiana is 
abundantly fertile in its native localities, but will not fructify, as Mr. Lindheimer informs me, in the 
gardens of the same region; Y. alozfolia, however, matures its pods more readily than any other 
species in Europe, where our moth cannot have an agency in it. We, therefore, are forced to assume 
that some other mode of fecundation, or even self-fertilization, can take place with them. Occasion- 
ally, no doubt, the moth performs its functions in the flowers of this species as well as in the capsu- 
lar Yuccas, Dr. Mellichamp has found its larvee tunnelling the seed rows of Y. aloifolia, destroying 
10 to 14 seeds during its growth, and eventually emerging through the characteristic perforations of 
the surface. He discovered also another larva in the green pods of this species, the egg of which 
- is evidently deposited into the rind of the ovary or young fruit, and which principally feeds on the 
immature pulp and only rarely attacks the growing seed. This, Mr. Riley thinks, must be the larva 
of a hymenopterous insect, which has, perhaps, nothing to do with the fecundation of the flower. 
But how may these Yuccas be fertilized without the action of the Pronuba? Probably, occasionally, 
and, so to speak, accidentally by other insects, or possibly sometimes by the withering and conniv- 
ing segments of the flower bringing adhering clumps of pollen in contact with the stigmatic juices in 
the open tube. Such chances, however, seem to be slim, not to say improbable, and in this case 
impregnation would have to take place on the day following the opening of the flower. 
t has been stated above that the quantity of pollen is small, and that the grains are large and _ 
somewhat viscid ; thus, when expelled from the contracting anthers, they remain in little clumps 
here and there within the flowers, on the papillose filaments, or, more frequently, attached to the 
inner surface of the perigon. When introduced into the stigmatic tube and in contact with its secre- 
tion, its tubes are developed, and, when we carefully dissect a fertilized ovary, large bundles of 
