PECAN KOSETTE. 19 
dwarfed, mottled, and roughened appearance typical of the second- 
ary phase. Dormant and axial buds of one to several series may and 
usually do prematurely develop into depauperate shoots, and toward 
the end of the season clusters of dwarfed branches are usually put 
out from dormant and adventitious buds farther back on the branches 
or main trunk. With each repeated sequence of premature abnormal 
growth and subsequent dying back of the branches, the new twigs 
and leaves tend to become more and more depauperate, so that a well- 
marked case of several years standing presents a characteristically 
gnarled appearance. 
HISTOLOGICAL AND CYTOLOGICAL STUDIES. 
No less striking than the external changes brought about by 
rosette are the. internal abnormalities of structure and metabolism 
in the leaf. The abnormal histological characters develop with the 
development of the leaf, and the most far-reaching internal derange- 
ments are found in cases of the greatest external malformation. 
Within the yellow thin areas between the larger side veins (second- 
ary stage) the tissue is usually less developed than normal, and the 
cells are more closely packed together (PL V, figs. A and B ; PL VI, 
figs. E and F). In less severe cases the palisade tissue is well de- 
veloped, but the intercellular spaces become almost obliterated (PL 
VI, figs. A, B, and D). In other instances the palisade cells are dif- 
ferentiated, but the individual cells are greatly shortened vertically 
(PL V, figs. B, C, and D) and may be only two or three times as 
long as broad, instead of seven to ten times, as in the normal leaf. 
In the most severely affected leaves with extreme variations in leaf 
diameter there is no differentiation into palisade and sponge tissue 
at all in the center of these yellow spots (PL VI, figs. E and F) , but 
the tissue within these parts of the leaf consists entirely of closely 
packed, more or less isodiametric cells without conspicuous air spaces. 
Under these conditions the number of cell divisions may be somewhat 
increased, the cells remaining smaller than normal (PL VI, figs. E 
and F). Usually, however, the number of divisions is reduced, and 
in some instances a parenchyma tissue only three cells deep has been 
found. (PL V, fig. A.) Occasionally the entire tissue between the 
margin and the midrib consists of undifferentiated cells. That this 
lack of differentiation is not due to immaturity was shown by ex- 
amination of young healthy leaves just after their emergence from 
the bud. Even at this } r oung and only partially expanded stage the 
palisade tissue of healthy leaves was found to be well differentiated 
(PL VII, fig. C). 
In the thickened portions along the veins, or sometimes throughout 
the lamina? in the aborted nonmottled leaves of depauperate rosettes, 
the size of cells may become increased in all three dimensions without 
