FURTHER STUDIES OF YUCCAS. 



221 



since the Agaves, with an entirely different sort of pollina- 

 tion, possess an equally copious stiginatic secretion. 



The Hesperoyuccas, represented by Whipplei and its 

 variety, appear to have undergone a greater adaptation 

 to general pollinators than the true Yuccas. Retaining 

 the stylar canal and septal glands of the prototype, 

 they have acquired a capitate stigma through the 

 consolidation of the spreading lobes, the small stig- 

 matic papilla) of other species becoming lengthened as a 

 means of catching pollen adhering to visiting insects. On 

 a few pistils, one of which is represented in the appended 

 figure, the stigma is, in fact, separated into its carpellary 



DIALYSIS OF HESPEKOYUCCA STIGMA, X 2. 



segments, each of which is strongly revolute. Similar 

 instances of dialysis have also been observed in the true 

 Yuccas, and these teratologic^ specimens represent pretty 

 nearly what I suppose to have been the original form of 

 stigma in the ancestors of the Yuccas. The pollen grains 

 may be assumed to have become somewhat viscid as a means 

 of surer attachment to visitors which did not go deliber- 

 ately to the anthers, and I am inclined to look on their 

 agglutination into crude pollinia as a result of this, — per- 

 haps intensified on the return of the plant to exclusive Pro- 

 nuba pollination, — rather than an original provision for 

 their bodily removal by other pollinators . These plants may, 

 therefore, have branched off from the earlier Yuccas after a 

 certain dependence on Pronuba had been formed, perhaps 



