2l8 THE TEACHING BOTANIST 



and bits of printed paper on slides are good. Every needful 

 operation of placing the stamen-hairs on the slides, peeling 

 epidermis, etc., should be done by the students ; and when 

 sections must be cut for them on the microtome, they should 

 have sections of their own also before them, so they may know 

 just what the former represent. 



Naturally, along with Exercise 39 a great deal of description 

 of function, etc., must be given, and from the start the fact that 

 the cell is essentially the protoplasm, and the wall but a 

 passive skeleton or box, should be made plain, as also that the 

 movement in Tradescantia is unusually rapid. Parts they can 

 see are, - - the circulating cytoplasm, full of food granules, the 

 nucleus, particularly important in reproduction, the vacuoles, 

 filled with cell sap, forming a reservoir of water and dissolved 

 food substances, and the containing wall. 



Under Exercise 40, the precise relation of guard cells to sur- 

 rounding cells is important as a point of observation ; also that 

 nuclei can be seen in epidermal cells, also that guard cells 

 contain chlorophyll. This is particularly good as an exercise 

 in observation. Students must be led to interpret the tissues 

 in terms of cells ; i.e. protoplasmic masses with walls, from 

 which, later, protoplasm may be withdrawn. 



Under Exercise 41, the drawings should show relation of 

 structures as magnified to those not ; i.e. it is better to have 

 students learn to represent just what place their most highly 

 magnified section has in the leaf, as shown on a piece of the 

 leaf unmagnified. Very important is the tracing of the aeration 

 (intercellular) system, its continuity through the leaf, and its 

 connection with the stomata. The palisade layers should be 

 represented as cells - - not as a shaded green layer. All of the 

 tissues should be studied from the point of view of function, 

 as a basis for which their knowledge of the conditions of 



