438 BOTANICAL GAZETTE [JUNE 
TABLE V 
DIAMETER FREQUENCIES OF XYLEM TUBES FOR SUCCESSIVE LEAVES OF REJUVENATED 
PLANT R; EACH UNIT REPRESENTS 3.3 u 
Diameters 
Leaf no. 
TiO} 2.5 | 2.0] 2.5 13-01 3;$ 1 4.01'4.5|'S.0 | 5.5 | 6:01 6.8 | 710) 7:51 8.01 8.5 
Pa S 44i3° | .25') 19 5 8 6 | 13 7.4 42 9 6 I 
Bees $ } 8 | to} 32 | 21 | 2s 8.) 29 S133 2.1.20 2 4 
6. 5} 206 y 2) TA) Baty 28) eee 6 
8 I 4°16 (io ):16 | 14 | 20°) 42 | Xs 7 1 Oe RE x 
10 QO baa 4 Fal 88 Vas oy i Ee 26 5 3 
SA SSS oie te ek ce . 3 6 9 | II § | x2 21% 7 Be ee Ute 
14 | AS EA as Ss OE BS One 2 al i We en ee a 
16 6 Pag eh 6 zr} xo 3 6 5 7 3 
| 
For comparative purposes, distortion figures have been worked 
out so far as trustworthy available data permit. These are based 
upon changes produced by senescence ' (original), depauperation 
(2), and moisture (20). It is to be regretted that the only estab- 
lished facts with regard to light are its axiomatic effects upon leaf 
position and the effect of darkness in stimulating the production 
of internodes. The method used in working out these figures 
should be apparent from inspection, and can be found adequately 
discussed by THOMPSON (19). 
In addition to these methods, microchemical studies were made 
throughout the summer of 1921 on tissues of 7. vulgare plants in 
all stages of senescence and rejuvenescence. 
Resvutts.—In general it will be noted that the percentage of 
dissection in various plants of T. vulgare tends to rise at a uniform 
rate. Studies of second year flowering plants indicate that after a 
value of 0.5 is attained, the degree of dissection fluctuates about 
that as an approximate mean until late in the flowering period. 
Then, as previously noted, if many leaves have been produced, 
the curve may rise to a higher value. 
With respect to T. laevigatum, fewer determinations are at 
hand and none are listed. All that have been made indicate that 
the rate of increase of dissection is not so rapid, but continues until 
a value of about 0.8 is reached, fluctuating about this value during 
the adult period proper. 
That the increase in degree of dissection is not merely a veiled 
expression of progressive decrease in leaf area is evident from fig. 5. 
