MANUAI, OF NATURE STUDY. 
113 
only in accordance with the peculiarity of the life 
dealt with. 
3. Study in proper season , exogens , endogens , 
ovary , anthers , pollen , germination , use 
of the pod . Make collections of exogen cut¬ 
tings not more than three or four inches long, 
tied in bunches as suggested for the collec¬ 
tion of buds. In fact the same collection will 
answer. What is the arrangement of woody 
matter in each case? Exogens have a bark made 
of an outer protective layer, a middle layer, and a 
green bast, or inner layer. Let pupils find these 
layers from a cross section. In the spring of the 
year when the sap is beginning to work, the cells 
out of which bark and fibre are both made, are so 
tender and soft, being filled with sap, that a very 
little pressure on the bark will cause the same to 
slip from the woody fibre. Boys sometimes make 
willow-bark whistles in the spring time, because 
of that fact. The growth of the stems comes 
from that layer of cells, one side building new 
green bark, the inner side building a new woody 
fibre. Plants that increase in size in that way are 
called exogens. 
Still examining cross sections, let the pupils 
observe that within the bark just described is woody 
fibre composed of bundles arranged in rings around 
a central pith. See if ali this is true of the apple 
