LEAVES 23 
amount of water given off by a few leaves is noted, some 
vague idea may be formed as to the amount given off by a 
great mass of vegetation, such as a meadow or a forest. 
One observer has 
stated that a single 
stalk of corn during 
its life (173 days) 
transpired about four 
gallons of water; and 
that a single hemp 
plant (140 days) 
transpired nearly 
eight gallons. An- 
other observer esti- 
mated that a sun- 
flower, whose leaf 
surface was approxl- 
mately nine square 
yards, gave off near- 
ly one quart of wa- 
ter in a single day. 
16. Growth.— In 
very young leaves 
growth takes place 
- Fic. 17.—Transpiration experiment: a potted gera- 
at the apex, but this nium sealed with a rubber cloth and covered 
may cease early. The with a bell jar; the mist and droplets of water 
on the glass more or less obscure the plant. 
subsequent growth 
often occurs at the base of the blade, in a special growing 
region, as may be seen in long and narrow leaves such as 
those of grasses. To discover these special regions of 
growth in leaves, some rapidly growing plants (such as 
the gourds) should be cultivated in pots. When the 
young leaves first appear, a scale should be marked off in 
India ink with a pointed camel’s hair brush on the petiole 
(if there be one) and the midrib. The scale should be made 
3 
