FURTHER STUDIES OF YUCCAS. 223 



in the related genus Prodoxus. The occurrence of such 

 rudiments in Prodoxus, however, is very interesting from 

 an evolutionary stand-point, for it points to the inference 

 that these moths are retrogressions from the Pronubas, 

 rather than a nearer approach to the common parents of 

 both. 



The three types of fruit on which the primary classifica- 

 tion of the true Yuccas rests, correspond with three modes 

 of dissemination in the genus. About half of the recog- 

 nized species have sweet, edible, pulpy fruit* ; two have in- 

 dehiscent fruits similar to the preceding during their early 

 development, but dry at maturity; and the remainder, 

 including nearly one half of the true Yuccas, and the Hes- 

 peroyuccas, have dehiscent dry capsules. All of these 

 fruits agree in their type of structure, as might be ex- 

 pected from the general uniformity in the parts of the 

 ovary in the several species. In all of those I have been 

 able to study during their development, the inner part of 

 the ovarian wall, corresponding to the superior face of the 

 infolded carpellary leaves, becomes more or less firm, the 

 walls of its cells being thickened and deeply pitted, while 

 the outer part is green and fleshy, and no doubt takes part in 

 the assimilative work of the plant. In the Sarcoyuccas, 

 this outer part becomes much thickened and quite succulent 

 and sweet toward maturity, assuming a yellowish or pur- 

 plish color and, in short, undergoing the usual ripening 

 process of baccate fruits. The seeds, meantime, in most of 

 these species, are immediately surrounded and protected by 

 the firm inner layer previously mentioned, which suggests in 

 texture and function the core of an apple, and in which 

 the seeds rattle with considerable noise when the fruit is 

 shaken. The pulp is easily removed from this core, which is 

 usually shaped to the convexity of the thick seeds, so that 

 when denuded it bears quite a strong superficial resem- 

 blance to a small ear of corn, a number of interspersed pale 

 and undeveloped seeds, causing a mottling suggestive of 



