2IO TRANS. ST. LOUIS ACAD. SCIENCE. 



fore led to believe that the few rare instances of yucca-fertilization in local- 

 ities where Pronuba may be presumed not to occur, have been brought 

 about bv another insect accidentally, or by the stamens reaching an excep- 

 tional length, and the anthers being brought into contact with the stigma 

 by the conniving of the closing petals. I have found the stamens of vary- 

 ing length in the flowers on the same panicle, and in some instances 

 almost as long as the pistil." 



Notes on the Genus Yucca. No. 2. 



By George Exgelmann, M.D. 



Since my paper on Yucca was published (pp. 17-54 ot this 

 volume) I have been enabled to make the following corrections 

 and additions : 



Page 20. The examination of more seedling Yuccas has proved 

 that the growth of the secondary axis and the young rootstock 

 exhibits the following forms : In Y. aloifolia as well as in Y. fila- 

 mentosa, var. Icevigata, I have found a single horizontal branch ; in 

 Y. angustifolia genuina and var. elata a single perpendicular branch 

 directed downward, and in Y. filamentosa genuina latifolia all the 

 young plants examined at the end of the second year exhibited 

 2-5 secondary axes directed downwards |to 2 inches and then 

 abruptly bent upwards. More observations' are needed about 

 these interesting peculiarities and their constancy in each species 

 or variety ; it is possible that the nature of the soil and the mode 

 of cultivation may have some influence on them. 



Page 26. The bunch of white wool is always present at the 

 tip of the perigonial lobes, but is very slight and short in some, 

 and longer and more copious in other species ; the hairs consti- 

 tuting it consist of single or sometimes of several cells. 



Page 27. Yucca Treculiana has, as is also stated on p. 43, very 

 thick ovules, and thus all Sarcoyuccas have such ovules and can 

 by them be readily recognized even in the flower and where the 

 fruit remains unknown. Y. gloriosa with its thin ovules does not 

 belong to this section at all, as will be shown below. 



Page 28. The stigmatic tube does communicate directly with 

 the three ovarian cells, but the passage closes immediately after 

 the night of flowering. 



