104 CARNEGIE INSTITUTION OF WASHINGTON. 



the egg-apparatus directly by means of waterj- solutions lying within 

 the locule. Furthermore, the embryo-sac is invested by a cuticle which 

 is discontinuous only for a small area at the apex, at which point the 

 gelatinous ends of the synergidse protrude. Only at this point might 

 watery solutions find ready entrance but for the above-mentioned 

 conditions. When the o\nales are dissected out and bathed with tap- 

 water, the synergidse absorb enough water frequently to burst inwardly 

 with respect to the embryo-sac, the vacuole disappearing. It may also 

 happen that the bursting results in extrusion of the synergidse from the 

 apex of the embrj^o-sac. The delicacy of adjustment of the sexual 

 mechanism thus indicated is further demonstrated by the fact that the 

 cells of the egg-apparatus and endosperm are plasmolyzed by a solution 

 of potassium nitrate slightly more concentrated than O.l/N. In plas- 

 molysis, the protoplasmic membrane, proper to the endosperm, lying 

 against the egg-apparatus is withdrawn therefrom, while the vacuoles 

 disappear by contraction from the egg and synergidse. It is this beha- 

 vior which shows that the entrance of the water into the embryo-sac 

 is through the uncuticularized apex. The difficulty of applying a 

 watery solution to the unprotected embryo-sac is apparent. 



It is, however, possible to reach the egg, as in Scrophularia, by inject- 

 ing the ovary. The course of movement of methylene blue lies through 

 the funicle and chalaza, and accumulation occurs in the tapetum, a 

 layer of cells investing the antipodal moiety of the embryo-sac. From 

 this region the reagent passes along the embryo-sac to the egg-appa- 

 ratus. That this behavior is perfectly definite is shown by the fact 

 that it is identical with that in orthotropous o\Tiles, of which a few are 

 usually found in each ovary. 



The course of the pollen-tube is as follows: Passing along the 

 mucilage cells of the placenta, it attacks the embryo-sac at the uncuti- 

 cularized apex, passing down between the tips of the synergidse to reach 

 to the egg-cell. The egg meanwhile loses its vacuolated structure, its 

 whole volume being occupied, the protoplasm having the appearance of 

 that of the pollen-grain. It is doubtful if fertilization involves the 

 destruction of one or both synergidse by the pollen-tube. 



Development and Persistence of the Fruit in the Cactacece, 

 hy Duncan S. Johnson. 



Work on this problem has been pursued during the current year at 

 Johns Hopkins University, and from April to September at Tucson 

 and Carmel. As in the past, chief attention has been devoted to the 

 origin, the anatomy, and the fate of the persistent fruits of Opuntia 

 fulgida. Studies have also been made of the persistence and prolifera- 

 tion of the fruits of other species of Opuntia and to the development and 

 distribution of the flowers of the giant cactus. 



