NOTES ON THE GENUS YUCCA. 197 



in tlie intervals and spare moments of a busy and exacting 

 professional life, Dr. Engelmann has made them tell most 

 effectively and advantageously upon the science which num- 

 bers him as a distinguished votary, by taking up one subject 

 at a time and investigating it as thoroughly as possible. In 

 this way he has mastered, in turn, our Cuscutcv, (upon which 

 his earliest essay was published in this Journal, thirty-one 

 years ago, and his latest was a full monograph of all the 

 known species throughout the world), our Cactacece, our JMis- 

 tletoes. Euphorbias, Junci, Callitriches, etc., not to speak of 

 several other genera or groups, or taking account of his sedu- 

 lous and long-continued study of our Oaks, and, above all, of 

 our Coniferce. Nor need we look to this as the close of the 

 series, but rather see before him " fresh fields and pastures 

 new," and wish for him more time to expatiate in them. 

 Upon the principle " to him that hath shall be given," he well 

 deserves it, as having accomplished far more in these rescued 

 moments than others who could mainly devote their days as 

 well as nights to scientific work. Almost without exception 

 these monographs relate to difficult subjects, and such as re- 

 quire long-protracted investigation. This is also true of the 

 present essay upon the genus Yucca. It is not a large one, 

 only a dozen species being clearly made out ; but those of 

 long cultivation in Europe have been much confused, and 

 recent ones described without flowers, while fruit is rarely 

 formed out of their native stations, and dried specimens of 

 any completeness are difficult to make, so that means of com- 

 parison are much restricted. 



The true anthesis, as is now shown, is nocturnal, the flowers 

 remaining half closed during the day. The anthers, witli 

 comparatively large and few grains of glutinous pollen, open 

 rather earlier than the flower. The tips of the style, whlcli 

 were naturally taken for stigmas, are now shown to be func- 

 tionless, the stigmatic surface being the moist and glutinous 

 lining of a stylar tube, which extends downward nearly to the 

 cells of the ovary and even communicates directly with them. 

 As soon as it became evident that fertilization must depend 

 upon nocturnal insects, it was found that they were most frc- 



