434 - BOTANICAL GAZETTE [yUNE 
REGENERATION.—Mere removal of older competing leaves 
does not alter the degree of senescent dissection of those subse- 
quently produced. Removal of all leaf incepts, down to undiffer- 
entiated meristem, results in production of juvenile leaves. The 
rhizomes produced by etiolation produce juvenile leaves when cut 
and placed in a moist chamber; in fact, after secondary thickening 
begins, pressure crushes the pith, and all rhizomes become essentially 
roots. Study of developing leaves shows that the juvenile leaves 
are produced by a disproportionate development of tip segment at 
the expense of the rest, while dissected leaves result from a more 
or less uniform development of all segments. 
Quantitative studies | 
MeEtTHopD.—More precise analysis of the réle of senescence as a 
cause of leaf dissection being desired, quantitative verification of 
these observations was obtained from studies of plants growing 
under widely different natural conditions. Prints of each successive 
leaf in each rosette studied were outlined by bounding polygons, and 
area of both leaf and polygon taken by means of a planimeter. 
The real area of each leaf was then divided into the differencé 
between real and ideal (polygon) area. This, it will be seen, gives 
a percentage expression for the degree of dissection of each leaf. 
It was finally deemed necessary, in order properly to delimit the 
problem, to investigate some of the correlations which more 
obviously suggested themselves. On the whole, these center 
about various phases of conductive efficiency of the xylem. Root 
cross-sections at various levels were studied to determine whether 
any correlation could be noted between cross-section areas and 
relative age of xylem tubes. Next the tube diameters were care- 
fully measured at the base of successive leaf petioles in a number of 
rosettes. These measurements were made with an eyepiece 
micrometer graduated to intervals of approximately 3.33 u- 
Since water conducting efficiency of a given cross-section of capil- 
lary tube is a function of the fourth power of its radius (18), the 
total capacity of each leaf was obtained by getting the sum, 
(diameter/2), of all its xylem tubes. Mean capacity represents 
this figure divided by the number of tubes in a given leaf. 
The ratio of total capacity to leaf area was also obtained in an 
effort to see whether it might be correlated with degree of dis- 
