PECAN EOSETTE. 
23 
In the large and small leaflets of single leaves a 94 per cent varia- 
tion in leaf area gave only 10 per cent variation in leaf thickness; 
but here again there was a 92 per cent variation in the area of the 
cross section of the vascular tissue, corresponding to the 94 per cent 
increase in the area of the leaf blade. (Table IV.) It will be readily 
seen that the differences in leaf thickness are at the lower range of 
variation found in normal leaves. In these juvenile leaves the varia- 
tion in area of the total cross section of veins was high, but not 
quite as great as the difference in leaf area : the area of the vascular 
part, however, increased in direct proportion with the size of the 
leaf, as would be necessary to carry an adequate supply of water and 
nutrients to and from 'the larger leaf blade. In these leaves very 
little variation was to be found in the vertical diameter of either 
palisade or spongy tissue. 
Table IT. — Tissue measurements as related to size in normal young pecan 
seedlings. 
Description of matenal. 
Thickness of Diameter of ^J£?gS£ 
tissue. large side veins, ^g 6 
Pali- 
sade. 
! jo. 
| crons. 
Large juvenile leavps 39 
First tvpeleaf above on same 
plants 40 
Large juvenile tip leaflets 35 
Small juvenile basal leaflets 
on same leaves 35 
Spongy. Total. 
Mi- 
crons. 
' 41 
30 
43 
39 
Vas- 
cular Total. 
part. 
Vas- 
cular 
part. 
Variation in 
areas. 
Cross 
section, 
vas- 
cular 
parts. 
Leaf. 
Mi- Mi- j Square Square Per 
crons. crons. [micron-?.. microns.' cent. 
515 351 207,460 96,211 
388 . 187 118, 215 27, 172 
538 351 j 227, 285 j 96,211 
243 103 45.987 8.171 
92 
Per 
cent. 
67 
Area of 
cross 
section, 
relation 
of vas- 
cular 
part to 
total 
veins. 
Per 
cent. 
The total area of the cross section of comparable veins in healthy 
leaves and in aborted leaves of approximately half size (PI. Ill, 
fig. D) was nearly the same for a given variety and set of external 
conditions. However, the area of the vascular portion of these veins 
was reduced from 43 per cent of the total area of the normal to 
about 33 per cent of the total area of the diseased veins. In the 
greatly aborted leaves (PI. Ill, figs. A and C) the area of the total 
vein cross section was about half that in the normal leaves, while 
the cross section of the vascular portion of these veins was only 10 
per cent of the total vein cross section as opposed to 43 per cent in 
the veins of normal leaves. (Table V.) While the area of total 
vein cross section, except in the most aborted leaves, tended to remain 
the same as in normal leaves, the development of vascular tissue 
within the vein became greatly reduced with the reduction in the 
