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, and the 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 all this is true of the apple 



