22 



BULLETIN 1038, U. S. DEPARTMENT OF AGEICULTURE. 



Table II. — Variation in the thickneHs of normal and rosetted pecan leaves, using 

 the thickest part of each leaf as the standard of oomparison. 



Description of material. 



Measurements of thickness. 



Average. 



Extremes. 



Variation 

 average. 



NORMAL LEAVES. 



Frotscher variety, Tliomasville, Ga.: 



North side of tree 



South side of tree 



Van Deman variet j', Cairo, Ga 



ROSETTED LE.^VES. 



Frotscher variety, Thomasville, Ga.: 

 Mottled leaves, about half size — 



North side 



South side 



Much-aborted leaves, south side — 



Nonmottled 



Mottled 



Linear leaves, south side — 



Nonmottled ; 



■ Mottled 



Mottled leaves, about half size, northeast side 

 Variety not stated, Cairo, Ga.: 



Mottled, red-brown stage, about half size 



Van Deman variety: 



Mottled, about full size 



Mottled, linear 



Microns. 

 162 

 147 

 168 



158 

 167 



1.52 



158 



lis 



11.3 

 139 



198 

 140 



Micron^. 

 131-187 

 122-173 

 154-187 



108-206 

 80-210 



70-215 

 72-229 



103-141 

 70-173 

 75-234 



140-281 

 78-195 



Per cent. 



38 

 37 



26 

 42 



26 

 50 

 55 



The average thickness of linear leaves was always less than that 

 of healthy or of other types of rosetted leaves. That this difference 

 is not normally related to leaf size was shown by measurements 

 comparing the thickness of the large juvenile leaves of normal young 

 seedlings with that of -the first type leaves above and that of large 

 tip leaflets with small basal leaflets on single juvenile leaves. (Table 

 III.) In the case of large juvenile leaves as compared with type 

 leaves above there was a 67 per cent variation in the area of the 

 laminse, but only a 7 per cent variation in thickness. In the vascular 

 portion of the large side veins, however, a 72 per cent variation in 

 the area of the cross section was correlated with this increase in leaf 

 size. (Table IV.) 



Table III. — Leaf thickness and vein diameter as related to size in normal 



young pecan seedlings. 



Description of material. 



Thickness (microns). 



Leaf 

 average. 



Leaf ex- 

 tremes. 



Large 

 veins. 



Leaf variation (per 

 cent). 



Thick- 

 ness. 



Area. 



Large juvenile leaves 



First type leaves above 



Large juvenile tip leaflets 



Small juvenile basal leaflets on same leaves 



103 

 96 

 112 

 101 



94 to 117 

 89 to 103 

 98 to 126 

 98 to 112 



515 

 388 

 538 

 243 



