May 2,1931 Effect of Ferrous Sulphate on Chlorosis of Conifers 165 
The primary leaves are approximately semicircular in cross section, and 
for the purpose of obtaining a comparative surface value were considered 
as halves of cylinders having a radius equal to the thickness of the 
leaf midway between the base and the tip, with the length equal to the 
length of the leaf. The perimeter of the cross section at this point was 
taken as irR+2R—that is, the sum of the lengths of the curved and 
the flat margins of the cross section. The surface of the leaf was 
taken as S = L(ttR+ 2R), in which L equals the length of the leaf. 
A sufficient number of primary and secondary 
leaves from each plant were measured to allow 
averaging (usually from 25 to 100, depending on 
the number per plant). The total primary leaf 
surface for the plant was obtained by multiplying 
the surface of the average leaf by the entire 
number of primary leaves. The secondary leaves 
were in most cases in fascicles of three, and their 
cross-sectional shape may be diagrammed as in 
figure 4. The same assumptions were made in 
this case as in the case of the primary leaves, 
the leaf being taken as an exact third of a 
cylinder with the radius equal to the thickness of the leaf midway 
between the base and the tip, and the surface calculated by the formula 
Fig. 4.—Cross-sectional 
shape of fascicle of three 
secondary leaves of western 
yellow pine- 
2R 
This formula appears to be more nearly correct than 
a paraboloid formula, and it is believed that it offers a better basis for 
comparing the leaf surface of one group of plants with that of another 
than would be given by statements of the average number, length, 
breadth, and thickness of the leaves. 
interpretation of the measurements 
From Tables III and IV it appears that the height and the weight of 
the tops, the length and the weight of the roots, the diameter of the 
stems at the root collar, the length and thickness of the secondary 
leaves, and the average total leaf surface of the plants was less for 
chlorotic plants than for green seedlings of the same vigor class and that 
terminal bud formation was most common and most pronounced in the 
most vigorous plants. The data indicate that the failure to form buds 
is related to a general lack of vigor, which in many cases is associated 
with chlorosis. The adverse effects of chlorosis on terminal bud fornia- 
tion and development is significant in connection with the high winter 
mortality of the strongly chlorotic seedlings. 
The small size of the different parts of the plants in the chlorotic 
seedlings, as compared with the green seedlings, is, on the whole, fairly 
uniform. Two exceptions to this are, however, noteworthy. In Table 
III it appears that the roots of the chlorotic plants are nearly as long 
