I04 Introduction to Botany. 



for a short time in water, and place it at the center of a 

 glass slip. Place at the center of a coverglass a small bit 

 of rotting wood or bark on which is growing a slime mould 

 Plasmodium (see page 252). The piece of wood or bark 

 should be so small that it will cling to the coverglass by 

 its own moisture. Put the coverglass with the object down- 

 ward over the hole in the felt paper, and set the prepara- 

 tion over a tumbler of water under a bell jar so that it will 

 not become dry. If the experiment is successful, the Plas- 

 modium will grow out over the coverglass, and may be 

 studied by transmitted light under high powers of the 

 microscope. Make notes on the streaming of the proto- 

 plasm. The batterlike plasmodium can be found at almost 

 any season of the year under the bark of moist logs or on 

 decaying leaves which have gathered to some depth in 

 damp woods. 



DISCUSSION. 



78. The Plant Cell. — When we examine very thin sec- 

 tions of the growing root tip of onion, for instance, under 

 a high magnifying power, we find that they are composed 

 of very small compartments, those near the apex being 

 very nearly isodiametric, while those farther back are more 

 or less elongated (Fig. 45, A and B). If we were able to 

 see through a whole root tip magnified to the same extent, 

 we should find that each of these compartments is really a 

 closed box to which, including its living contents, the term 

 rcN has been applied. The walls of the cells of the onion 

 root tip are composed of cellulose, a substance well suited 

 to form the walls of growing cells, for it can stretch and 

 allow the cells to enlarge, and it permits liquids and gases 

 in solution to pass through it readily. It is not alive, but 

 has been manufactured by the live parts of the cell. The 



