396 Field, Forest, and Wayside Flowers 
as we have seen, travels via the young wood ; elab- 
orated sap moves through the inner bark or 
‘* bast,’’ where, in most trees, a way is prepared for 
it through what are technically known as “‘ sieve- 
cells.’” These are long and narrow, and run length- 
wise of trunk and boughs. 
As the sap moves through them, it comes to 
places where the partition-wall between cell and 
cell is ‘‘ punched full’’ of holes, like the top of 
a pepper-pot. Fine fibrils of plant-jelly reach 
through these, joining the contents of neighboring 
cells, and in summer, plant-fluids pass easily all 
along the route. But as autumn approaches, Nature 
seals these holes and isolates the ‘‘ sieve-cells.’’ 
About midsummer, a glutinous plate, called the 
callus-plate, begins to form upon the little sieve, 
stopping up its pores. This gains thickness and 
solidity all through the waning of the year, and by 
time the leaves fall the route through the sieve- 
cells is closed as completely as is the route to Klon- 
dike in midwinter. This sealing of the little 
sieves has a beneficent purpose. At almost any 
‘time throughout the winter, in our latitudes, we 
may have a false promise or mocking similitude 
of early spring. We have seen that several gulli- 
ble or foolhardy herbs may be cheated or dared 
