96 The Wateri.iues. 



broad, placed so that one end touches the rhizome and the other is a very 

 short distance above. These are the stipules. In a leaf 0.64 cm. long the 

 lamina is still more than twice the length of the petiole ; the inrolled sides 

 now meet in the median line and the veins are prominent. The lobes of 

 the leaf extend down along the front of the petiole and are slightly divari- 

 cate. The petiole is about as broad as long and somewhat contracted at 

 each end. The stipules are slightly larger and more nearly vertical. The 

 coating of hairs on petiole, stipules, and lamina is well developed, and the 

 swollen collar at the base of the leaf is becoming evident. Subsequent 

 development is, to outward appearances, chiefly a matter of size, except 

 with regard to the stipules. On a leaf of N. rubra whose petiole is 

 already more than 5 cm. long these form lunate auricles, with nearly verti- 

 cal line of attachment to the petiole, and a lobe extending upward a short 

 distance above the line of insertion. Such a stipule is about one-third as 

 wide as the diameter of the petiole and twice as long as wide. After this 

 it decreases in proportionate width, while greatly elongating to reach the 

 mature form. In N. odorata (PI. II) and N. alba the young leaf rudiment, 

 less than 0.16 cm. in length, is more rounded and less acute than in N. 

 rubra and the stipules are quite different. About the time the flattening 

 of the inner side of the rudiment to form the lamina occurs, two elongated 

 ridges appear, one on either side of the base of the leaf, extending along 

 toward each other just in front of the rudimentary petiole. The adjacent 

 ends soon meet in the median line and the beginning of the stipular plate 

 of the Castalia group is evident. Being shorter in the median line than 

 at the sides, its outline is obcordate. As the whole ridge grows higher, it 

 overtops its leaf at the length of about 0.3 cm., and on either side of the 

 middle line an S-shaped fold occurs, which throws the median part of the 

 stipules away from the leaf, or, to state it otherwise, forms a groove into 

 which the leaf fits. A great thickening along these folds makes two 

 strong keels on the inner side of the stipule. Later this broad plate 

 elongates to the typical adult form. A leaf rudiment oi N. odorata 0.3 cm. 

 long had downward pointing hairs covering the back of the lamina and the 

 petiole, but on the next younger leaf these were present only on the lamina. 

 The formation of the principal air-canals takes place at an extremely 

 early period. The first beginning of separation of the cells was seen in 

 N. caerulea in a rudiment 0.5 mm. long. The canals were seen with the 

 naked eye in a leaf rudiment of N. flava about 1 mm. long ; the bounding 

 walls were composed of columnar cells. At 1.6 mm. long all of the canals 

 are indicated. In the smaller leaf the fusion of the three main bundles 



