IN TR OD UC TION. 1 5 



VII. CARE AND USE OF MATERIAL. 



Throughout the directions for laboratory work it is 

 understood that material preserved in alcohol will 

 answer unless otherwise stated. In many cases only 

 alcoholic specimens are usable and in other cases only 

 fresh specimens. 



Do not tear up specimens needlessly. 



Examine a specimen thoroughly and see as much as 

 possible before dissecting. 



Do not begin dissecting a part until it is decided 

 what to look for and where to look for it. 



Be economical ; chiefly because it is a good habit, 

 secondarily because material costs time, or money, or 

 both. 



Save the pieces ; they may be useful in future work : 

 it is easy to throw away ; it is more difficult to gather. 



Preserve all sections and other preparations until the 

 study of the plant is completed. 



When the specimens are mounted in water be care- 

 ful lest they become dry by the evaporation of the 

 water. It can be most conveniently replaced by plac- 

 ing a brush charged with water at the edge of the 

 cover opposite the area of air. As soon as the air is 

 displaced the brush should be removed. 



When studying particular tissues in a section the 

 thinnest parts of each tissue should be selected. It is 

 rare that a section is so uniform that the tissues are 

 equally well shown in all parts of it, and different tissues 

 must not infrequently be looked for in different sec- 

 tions. It is best therefore to look well over the speci- 

 mens before settling to the study of any tissue. 



In order to obtain a clear conception of the shapes 



