Reed and Smoot : Polygonum virginianum 



381 



thicker layer is composed of compact sclerenchyma elements, 

 which have been described by Sirrine ('94), and the inner layer is 

 composed of long, woody fibers, which are in close contact with 

 the sclerenchyma wall. At the apex of the achene the fibers of 

 the inner wall are continued outward and downward, forming the 

 tissue of the persistent style. The whole structure of the achene 

 gives to it sufficient mechanical strength to resist fracture at all 

 points except the specially constructed separation-layer. 



Certain indications of a separation-layer in the pedicel are 

 evident from a very early stage. The youngest flower-stalks ex- 



Fig. 3. Diagram of a median longitudinal section of a pedicel at the time of ma- 

 turity. v4, epidermis; B, cortex ; C, sclerenchyma ; D, tlbro-vascular bundles ; £, 

 pith; ^separation -layer; /, cushion of thin-walled pith-cells ; M, sclerenchyma-layer 

 of achene-wall. 



amined seemed to indicate that the pollen-mother-cells had recently 

 accomplished the second division. In such sections one may dis- 

 cern a zone of short cells extending across the pedicel a short dis- 

 tance beneath the base of the macrosporangium. The cells of this 

 zone are thin-walled and parenchymatous like the other cells of 

 the young pedicel. At the same time, or very shortly afterward, 

 the pedicel is slightly constricted in the region of this zone. 



As the flower approaches the time of blossoming the cells of the 

 pedicel undergo differentiation into the tissues described above. 



