248 ELEMENTS OF BOTANY. 
and the sketch which the pupil is making, —all while the work is 
going on. But if the class unfortunately consists of from twenty- 
five to forty pupils, in an ordinary recitation room, a good deal of 
ingenuity will be needed to secure results of any value. 
The microscopes with the prepared objects should be placed upon 
the desks or tables which are best lighted. 
If there are several instruments it will usually be found preferable 
to use all of them during any given recitation upon preparations of 
the same object, but to have some provided with lower and others 
with higher powers. 
It is important to have a card attached to each microscope stating 
what object is upon the stage and what magnifying power is given 
by the combination in use. The class may sometimes be divided and 
half, or less than half, be allowed to work with the microscope while 
the rest are engaged in written or oral recitation, or in examining 
the gross anatomy of the seed, root, stem, etc. Each student should 
be required to take his note-book to the microscope and draw while at 
the instrument. 
Several of the best sketches may be put on the board toward the 
end of the hour, and a composite drawing finally made, embodying 
the best portions of each. A still better plan is to have posted at the 
last a drawing which the instructor has prepared beforehand (best 
with the aid of the camera lucida, or from a photo-micrograph), and 
if desirable to have this copied by the class. The object sought 
should be to make the pupils see as much as possible for themselves, 
but to make sure before leaving the object that they see it as it 
really is. 
Magnifying Power.— The lowest magnifying power which will 
show the desired structure is to be preferred, both because this admits 
of the best illumination and because an average focusing which will 
suit most of the eyes in the class can be secured with objectives of 
Z-inch or longer focus, but not with higher powers. Constant use 
should be made of the 11-inch or 2-inch objective to give general 
views of the object. A double nose-piece with 2-inch and 4-inch, 
or l-inch and 14-inch objectives attached will save much time and 
trouble. 
The class may best be made to understand the meaning of the 
