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 IV.- 



-Tissue measurenients as related to sise in normafl young pecan 

 seedlmgs. 





Thickness of 



tissue. 



Diameter of 

 large side veins. 



Area of cross 



section, large 



side veins. 



Variation in 

 areas. 



Area of 



cross 



section, 



relation 



of vas- 



cular 



part to 



total 



veins. 



Description of material. 



Pali- 

 sade. 



Spongy. 



Total. 



Vas- 

 cular 

 part. 



Total. 



Vas- 

 cular 

 part. 



Cross- 

 section, 

 vas- 

 cular 

 parts. 



Leaf. 



Xarge juvenile leaves 



First typeleafabove on same 

 plants 



crons. 

 39 



40 



35 



35 



Mi- 

 crons. 

 41 



30 



43 



39 



Mi- 

 crons. 

 515 



388 



538 



243 



Mi- 

 crons. 

 351 



187 



351 



103 



Square 

 microns. 

 207,460 



118,215 



227,285 

 45,987 



Square 

 microns. 

 96,211 



27, 172 



96,211 



8,171 



Per 



cent. 



\ - 



[ 92 



Per 



cent. 



67 



94 



Per 



cent. 

 i 46 



1 23 



Large juvenile tip leaflets 



■Small juvenile basal leaflets 

 on same leaves 



1 " 



1 18 







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 (PL III, 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 



