20 
BULLETIN 1038, IT. S. DEPARTMENT OF AGRICULTURE. 
essential change in ratio between spongy and palisade tissue. (PL VI, 
figs. G and H: Pis. VIII and IX.) In some cases a slight increase 
in number of cell divisions also takes place (PL VI. fig. E). The 
individual cells appear abnormally healthy, and increase in leaf 
thickness here is due largely to increase in size of the individual cells 
(Table I). Along with this increase in cell size there is a reduction 
in size of intercellular spaces within the spongy parenchyma, and in 
the severely attacked leaf an almost complete obliteration of air 
spaces results (PL VT 3 figs. B to F). 
Table I. — Tissue and cell measurements of normal pecan leaves compared icith 
those of leaves hypertrophied with rosette. 
Tissue and cell measurements (microns). 
Variety and leaf tissue. 
Normal. j ""g*^"* , Rosette, aborted. 
Rosette, 
linear. 
Protscher variety, Thomasville, 
Ga.: 
Palisade rells... dimensions.. 
50 to 52 by 5.5 to 6. 
STtolOO 
57 to 60 by 6.5 to 9.5 58 to 67 bv 8.5 to 10 . 
Spongy tissue. ...thickness.. 
Spongy tissue where palisade 
tissue is lacking: 
Upper epidermis 
76 to 116 
114 to 116 
33 to 65 
61 to 70 
9.4 to 12.6 
10 to 12.2 
11.2 to 14 
"..".- thickness. 
Lower epidermis. . . do 
Van Deman variety, Cairo, Ga.: 
10.3 to 11 
10 to 11 
9.4 to 11 
53 
69 
57 
Spongy tissue do 
84 
125 
94 
Linear leaves may or may not show a differentiation into palisade 
and spongy tissue, but where the palisade cells are developed they 
are usually shortened vertically and the spongy cells of the paren- 
chyma are more closely packed together than the cells in healthy 
leaves (PL V. fig. D). The average thickness of these leaves tends 
to be less than normal and this reduction is due partly to decrease 
in the number of cell divisions and partly to the shortened vertical 
axis of the palisade cells. The elongated shape of the leaves, how- 
ever, is not due to variations in cell shape but rather to a decrease 
in the number of cell divisions in which the central spindles are 
perpendicular to the midrib. This would tend to keep the cells closer 
to the main water supply of the leaf. 
Amelung (9) working with plants and Conklin (25) working 
with animals have shown that normal tissue cells of corresponding 
organs or parts of organs within a species or variety are in general 
of the same size and that the size of organs is primarily due to 
differences in the number rather than in the size of cells. Mrs. 
Tenopyr (77). as a result of investigations in several species of 
plants, found that difference in the shape of leaves of the same 
plant or related species is not correlated with difference in the shape 
of their cells. Linear leaves are not composed of longer, narrower 
