THE PLANT SKELETON. 



131 



K 



P 



B 



Fi«, 36.— Cross section of false Ciuuamon sliow- 

 inKoorky forinaiions. (Moeiier). 



genie or pericambiiim origin, there may 

 also be found collenchyma, sclerotic 

 eellSj bast fibres, crystals, resin passages 

 and oil cells. When the entire periderm 

 is made up of such diverse elements it 

 has been termed bark, (a) 



Pharmacognocists recognize three parts 

 in barks. The Outer, Middle and Inner 

 Barks, The Outer bark includes the 

 corky epidermal layer* on the outside of 

 the stem; the Middle bark is what re- 

 mains of a portion of the primary epi- 

 dermis, it becomes quite complex and 

 contains a variety of substances^ crys- 

 tals, chlorophyll, tannins, oil, etc. The 

 Inner bark lies between the middle bark 

 and the cambium and is traversed by the 

 medullary rays of the phloem, 



MECHANICAL TISSUES, OR THE 

 PLANT SKELETON, These tissues 

 are developed by the plant for the pur- 

 pose of internal protection of the more 

 delicate growing and conducting tissues. 



against internal and external pressures 

 both above and below ground. 



The most important mechanical tissues 

 are Sclerotic Cells, Collenchyma, Wood 

 Fibres and Bast Fibres, The word 

 Stereom expresses these cells taken col- 

 lectively* 



M 



Fig. 37.— Cross section of bark of Canella alba. 

 ^. outer bark, with ^- cork. /jA phelloderm, M. 

 middle bark with suberized oil reservoirs and 

 crystals, /. inner bark with medullary rays which 

 contain crystals of calcium oxalate, s. obliterated 

 sieve tube elements. (Tfcchiich). 



Sclerotic Cells. Sclereids, Stone Cells. 

 These are thick cells varying from iso- 

 diametric to oblong, round, oval or ir- 

 regular in shape. They are strongly lig- 



(a) J. Moeller, Die Baum rinden, Berlin 

 1882. 



Fi^.r 38,— Stone cell from Pimenta, 

 stratification and branched pore 

 tTscbirch). 



showing 

 dmals. 



