37° 



BOTANICAL GAZETTE [November 



consecutive primordia. Evidences indicate that a scale is not pre- 

 determined, but remains abortive through some variable cause. The 

 primordia, whether developing scales or leaves, show the same struc- 

 ture in every particular. 



The leaf traces. — The course of the leaf traces in the seedling are 

 the same in general plan as those described for the embryo, but the 

 girdling in the older leaves and scales is much more marked. ' The 

 internal growth and the appearance of new organs has crowded the 

 older parts farther and farther outward. The circumference of the 

 cortex has increased materially, and also the length of the vascular 

 strands running through it. In the older scales and fully developed 

 leaves these are all of about the same extent, and almost horizontal; 

 but from these, through the younger leaves and scales to the youngest 

 primordia, the sweep of the girdle diminishes; but the girdles are 

 already established in the very youngest of the primordia (figs. 34, 35, 



Ug.) 



Although in the strands of the youngest leaf primordia no xylem 

 elements are present, the courses of the bundles may be made out 

 readily because of the arrangement, the staining qualities, and shape 

 of the cells, which have denser protoplasm and larger nuclei, and are 

 longer than the adjacent cells (figs. 26, 27). The strands of the very 

 youngest primordia which have their origin on the opposite side of 

 the central cylinder show the girdling habit in the same manner as 

 those of the older leaves, but on a smaller scale. The girdle does 

 not always take the horizontal direction, but may be more oblique at 

 the beginning (figs. 4, 5, 34, 35). Fig. 35 shows this clearly, in which 

 pc is the procambium and Ug 1 the girdle of the youngest primordium. 

 So long as such a strand is outside of the procambium it can be followed 

 easily, but is lost after it has entered it. 



In the oldest plant examined (three or four years old), the first, 

 second, third, and fourth leaves displayed exactly the same condition 

 as was shown in the young leaves of the embryo and seedling. But 

 in the older leaves, outside of these, it is impossible to determine 

 whether the described order is retained, because of the difficulty in 

 following up strands of such size; but it is certain that anastomoses 

 are more frequent, due to the close proximity of crossing bundles. 



The transition of the xylem. — The strands of the older leaves have 



