IS THE VALVE OF UTRICULARIA SENSITIVE? 151 



to the axis of the leaf. Often one can follow the dif- 

 ferent steps by observing on a single leaf their develop- 

 ment from the base to the tip. The utricle, which at 

 first is filled with cytoblast, becomes by rapid absorp- 

 tion changed to an air-vessel. By its further extension 

 in all directions the utricle approximates more and more 

 to its future form. It becomes flattened, and assumes 

 the form of a stomach, the stalk is at the pylorus, the 

 opening at the cardia. On the greater curvature both 

 walls come together as if at a seam. The opening of 

 the perfect utricle is, according to Benjamin, provided 

 with a little flap turned inward, which he calls the 

 vafoe. This valve appears in the earliest state of the 

 utricle as merely a cluster of dark cross stripes. . . . The 

 side walls of the young utricle grow rapidly; the air 

 cavity which they contain becomes thereby greater. 

 The edge of the lateral walls approach each other and 

 bend inward ; the original opening becomes closed, and 

 exhibits the dark stripes described by Benjamin. The 

 flap on the valve consists of the wall bent inward on 

 that part of the utricle turned away from the stalk. 

 On the side turned towards the stalk the edge is not so 

 strongly developed. . . . The full-grown pouch presents 

 itself as a roundish and somewhat laterally compressed 

 body, which above_ is continuous by one angle with the 

 stem, while the other exhibits an orifice which forms a 

 little funnel projecting inward. The external orifice of 

 this funnel is closed by a rim of beard growing on the 

 upper border; the lower part of the internal surface 



