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THE POPULAR SCIENCE MONTHLY 



similarly difficult and complicated oviposition of the Cynipidce, as 

 Adler has shown. In dissecting the young fruits of the filamen- 

 tose yuccas, with a view to critical examination, I have found 

 that about half of them, on the average, contain nothing; but the 

 proportion varies greatly in different localities and according to 

 circumstances, and I may say that, as a result of my numerous 

 examinations, fully two thirds of the mature pods are found to 

 contain the larvae of Pronuba. All the experiments which I have 

 so far made, or have known to be made, prove conclusively that 

 the capsular species never set fruit without her aid. 



Pronuba yuccasella is found in all parts of the country east of 

 the Rocky Mountains where the filamentose yuccas normally 

 range ; but has not extended to all sections where they are culti- 

 vated. The time of its appearance is strikingly coetaneous, east 



Fig. 10. Mature Pods of Yucca angustifolia : a, artificially pollinized and protected from 

 Pronuba ; b, normal pod, showing constrictions resulting from Pronuba puncture and exit- 

 holes of larva: c, one of the lobes cut open, showing larva within. 



of the Mississippi, with the blooming of filamentosa j while other 

 cultivated species which bloom either earlier or later, and which, 

 therefore, do not receive the visits of the moth, I have, as already 

 stated, never known to bear seed. On the Western plains, where 

 Y. angustifolia is native, the moth's season of appearance is 

 adapted to the flowering of this particular yucca. In California, 

 Yucca whipplei is pollinized by Pronuba maculata, an invariably 

 maculate species ; while, on the Mojave Desert, Yucca brevifolia is 

 pollinized by Pronuba syntlietica, a species still more abnormal 

 than yuccasella and modified to fit it to the peculiarities of that 

 particular species of yucca. In the Gulf States the typical yuc- 

 casella occurs, and fertilizes not only the filamentose yuccas, but 



