ELLIOTT: VARIATIONS OF QUERCUS. 51 



concentric bands, while in Nos. 1 and 2 the xylem and phloem 

 bands are broken, so that the vascular system is in three 

 bundles. The middle bundles vary greatly in shape, but there 

 is considerable variation in this respect in different petioles 

 from the same individual oak. 



Figures 27 to 30 show cross sections of the midrib of the 

 leaves taken at two-thirds up from the base of the blade and a 

 little above the insertion of a vein, which accounts for the bast 

 ring being broken. The sections show that the middle bundle 

 of Nos. 1, 3 and 4 have disappeared, while that of No. 2 still 

 persists. 



Cross sections were made on the hand microtome, from 

 material preserved in formalin, to determine the manner and 

 place of the ending of the middle bundle. This method was 

 used as being better than embedded material in keeping the 

 exact position of each section taken. My fellow student, F. 

 W. Mulsow, found that a mixture of safranin and hsema- 

 toxylin makes a very good double strain and greatly shortens 

 the process for temporary mounts. A section can be kept on 

 the point of a needle, dipped in the double strain for a few 

 minutes, washed in seventy per cent alcohol, and mounted 

 in glycerine, with very satisfactory results. 



The middle bundle of No. 2 ended a little above two-thirds 

 the length of the leaf, that of No. 4 a little below two-thirds the 

 length, and that of Nos. 1 and 3 a little above one-half the 

 length of the leaf. The size of the leaf and midrib made no 

 difference in the relative distance the middle bundle ascended 

 the midrib. At the point of ending of the middle bundle in a 

 large leaf the midrib might be larger than the midrib at the 

 base of the blade in a smaller leaf. 



The branching of the midrib into the lateral veins has an 

 indirect effect upon the middle bundle, as the bundles break 

 up into sections whenever a branch is given off, and in the 

 readjustment a portion of the middle bundle is attached to 

 the upper bundle. The middle bundle does not branch directly 

 into the secondary veins. The termination of the middle 

 bundle in No. 4 is distinctly different from that in the other 

 three oaks, as the middle bundle in No. 4 always disappears 

 by joining to the side of the upper bundle, while the juncture 

 in the other three is in one manner or another always made 

 at the middle of the upper bundle. The manner of joining 



