43 
the subsequent exposure to the moist air led only to a coloration of the 
veins. The lamina remained green. The simultaneous effect of heat 
and of drying up must unite, therefore, to produce the phenomena 
observed in “sunburned” leaves. - 
“WHITE VEINS.” 
The phenomenon of ‘‘white veins” is observed in the curing barn 
after a long spell of dry and warm weather. The veins then lose the 
capacity of turning brown on the surface, and preserve a whitish or 
rather colorless appearance after the curing process isover. On holding 
such a leaf between the eye and the light, a sufficiently dark-brown 
coloration of these veins is plainly seen, hence it is only the surface 
which is devoid of coloring matter. There is hardly any other expla- 
nation than that by a too rapid drying the epidermis cells of the veius 
died too quickly and this premature death caused the entrance of air 
into and perhaps also below them,' leading to the optical illusion that 
coloring matter is absent in the veins, although the interior cells (those 
of the vascular bundle) contain it.2. The microscope reveals colorless 
and air-containing tissue around the brown sieve-tissue masses in the 
“white veins,” while in the normally colored veins the tissue surround- 
ing the sieve tissue is more or less yellowish brown. The presence of 
‘‘white veins” decreases the value of the wrapper leaf, while it has no 
influence upon the value of the fillers. On the contrary, such fillers 
may often be very valuable. To prevent the ‘‘ white veins” there seems 
no other way possible than to keep the barn closed in prolonged hot, 
dry weather and to occasionally sprinkle water through the barn. 
“SALTPETER” ON TOBACCO. 
A phenomenon resembling to some extent that of ‘‘white veins,” but 
in reality very different from it, is the efflorescence of a white saline 
mass upon the midrib and lateral ribs of the curing tobacco leaf. The 
tobacco planters and manufacturers call it ‘“saltpeter,” but sometimes 
there are only traces of saltpeter (nitrates) found in these efflorescences. 
They contain principally a mixture of potassium, sodium, calcium, and 
nicotine salts. The writer has not chanced to observe an efflorescence 
consisting only of saltpeter, although the possibility of such an occur- 
rence can not be denied. The phenomenon is probably caused by a 
long spell of dry weather in the first stages of the curing. 
Finally, it may be mentioned that sometimes a white mycelium of 
some fungus makes its appearance on the veins of the curing leaf, 
1Such a phenomenon is also frequently noticed in August on the leaves of the 
peach tree, as Dr. Galloway has kindly pointed out to the writer. 
2Mr. Floyd reported to the writer that occasionally white veins are also notice- 
able in plants while growing in the fields, and that in such cases the leaves are 
usually of a very dark green. 
