96 THE NATURE-STUDY OF PLANTS 
require roughly 8000 of the same size to cover one 
square inch. I should mention that there are few 
or none at all upon the upper surface of the leaves of 
this plant, but at this rate for every square inch of 
leaf there are on the underside 80,675 pores, and on 
a well-grown leaf a full half-million or more, according 
to its size. 
Now, it is not easy to realize what 80,000 things of 
any sort would look like if seen all at once. Ona 
field of five acres 80,000 people would form a dense 
crowd : a pile of 80,000 halfpennies would be consider- 
ably taller than St. Paul’s Cathedral, for there would 
be more than 10,000 of them left over; a nice little 
sum, to be exact, of £21 1s. 4d., and it would be as 
much as or more than most of us could do to carry 
half of it a few yards, for five pounds’ worth of half- 
pence weighs fully thirty pounds. 
If we arranged the 80,000 coins in a square its 
sides would measure about eight yards, and if we 
started on Monday and counted for two hours a day 
at the rate of 100 a minute, instead of having a 
holiday on the following Saturday we should have to 
put in extra time to the extent of one hour twenty- 
six minutes and three-quarters in order to finish 
counting the pores on one square inch of leaf before 
Sunday came. Two hours for five days and three 
and a half on the sixth, and then we should only have 
done about one-seventh of a well-grown leaf. 
So I think there can be no doubt that those of the 
Herb Robert are not likely to be suffocated from 
want of breathing pores. 
It may be of interest to turn for a moment to the 
pipes which, as I have said, run through the whole 
bedy of the plant, carrying water and dissolved salts 
