Page:Popular Science Monthly Volume 41.djvu/191

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179
THE YUCCA MOTE AND YUCCA POLLINATION.

spines on the back, which are well fitted to enable it to work its way to the surface from its underground retreat.

The effect of the puncture of the female moth in oviposition is at once noticeable on the young fruit by a darker green discoloration externally. In time this becomes a depression, and the irregularities of the pods (Fig. 9, d, e; Fig. 10, b, c) which have been considered characteristic of the fruit of the genus are chiefly due to these punctures, which, ordinarily occurring just below the middle of the pod, produce a more or less marked constriction there.

PSM V41 D191 Components of the yucca filamentosa.jpg

Fig. 9.a, longitudinal section of pistil of Yucca filamentosa, showing (b, b) punctures of Pronuba, and (c, c) the normal position of her eggs in the ovarian cell; d, section of a punctured carpel seven days after oviposition, showing the egg yet unhatched and the manner in which the ovules in the neighborhood of puncture have been arrested in development so as to cause the constriction; e, section of an older carpel, showing the larva above the original puncture; f, a seed thirteen days from oviposition, showing young larva at funicular base.

This I have often proved by artificially pollinizing the flowers and protecting them from Pronuba, when the pods will develop in a regular, parallel-sided manner (Fig. 10, a).

It is noticeable that all the pods do not contain Pronuba larvæ, though we rarely find any on the filamentose species that do not show the marks of puncture, which indicates that a great many punctures are fruitless in result, owing either to the difficulty of the operation of oviposition, or to the fact that the eggs, having been once consigned to the pistil, have failed to hatch, for one reason or another; or again, that the larva has, for one reason or another, perished. A similar mortality is connected with the