PROCURING OBJECTS. 



71 



simple form of vegetable life. Its primary development may 

 be seen by examining a small portion of yeast at intervals 

 under the microscope. No plant is without cellular tissue, 

 and many are destitute of any other kind of tissue, as the 

 lichens, and some fresh-water algae. A section of the pith of 

 elder, pulp of peach, &c., will afford specimens. 



The petals of flowers are mostly composed of cellular tissue ; 

 their brilliant colors arise from the fluid contained within the 

 cellules. These form excellent microscopic objects, and when 

 mounted in balsam are permanent. The pelargoniums and 

 geraniums are among the most interesting. 



The petal of the anagallis, or scarlet chickweed, is a beauti- 

 ful object. The spiral vessels diverging from the base, and 

 the singular little cellules which fringe the edge, are worthy of 

 notice. 



Cells differ in form according to the mode in which they are 

 aggregated, a, Fig. 24, represents the dodecahedral and 



Fig. 24. 



dotted cells in the pith of elder. Cells are either surrounded 

 by a simple membrane, or by thickened walls. The thicken- 

 ing of the wall takes place by a deposit of woody matter on 

 the inside. Occasionally, portions of the cell-wall are left un- 



