TO 



THE PRINCIPLES OF AGRICULTURE. 



of ])lants, and often also in different parts of the same 

 {)lant. In their simplest forms they are generally spher- 

 ical, or globular. In the fiber of wood they are long and 

 ta})eriiig, lirnily jcjincd together by their sides. 



in fill H¥ 



l\Vi \ 



r -^r- 



Section of Wood. 



Lengthwise Slice of ]V<md //■om 0,1 Ailunlhiix glmKhdoaa, or "■ Tree of Heaven,'' 

 h if/hi !/ miignifled. 



Sometimes the covering of the ends of these long cells is 

 removed, so that they oyvn into each other, and form a con- 

 tiniious tube, through Avhich the sap may flow more freely. 

 Fibers of cotton and flax arc simply long, single cells. 



