MICROSCOPIC STRUCTURE OP WEED SEEDS 527 



Curled Dock (Bumex crispus L.). 



The brownish achenes of this species consist of an epidermal 

 layer of elongated cells with thick stratified walls, outer wall 

 colorless and a thick cuticle. The underlying parenchyma cells 

 of three rows are smaller, with thick, brownish walls; cells contain 

 tannin. The testa consists of two layers of cells, one large, thin- 

 walled with brownish walls, the other compressed. The endosperm 

 cells are large, thin-walled, and contain simple starch grains. 



Lady's Thumb or Smartweed {Polygonum persicaria L.). 



In this species the palisade cells are long, narrow and truncate. 

 The cell cavity extends the whole length of cell at the upper end, 

 with prominent branching pore canals. The sub-palisade portion 

 consists of four layers of small roundish cells, a small chainlike 

 layer also between the sub-palisade and endosperm. The endosperm 

 consists of large irregular cells. Measurements: 138.6/*; palisade 

 cells, 108.9m ; sub-palisade, 29.7m. 



Knotweed (Polygonum erectum L.). 



In this species the "palisade cells" are much broader than in 

 the other species here described. The cells have irregular papillate 

 projections as in P. dumetorum var. scandens. The cell cavity is 

 narrow with long canals extending from it; cavity branches divide 

 near the end of the cell. In P. erectum the whole cell is of a light 

 brown color while the cavity is colorless. The sub-palisade portion 

 consists of two layers of isodiametric cells. The endosperm has 

 long, narrow, regular cells. Measurements: whole seed coat, 82.5m ; 

 palisade cell, 60; sub-palisade, 22.5m ; papillate projections, 3.3m. 



Smartweed (Polygonum hydropiper L.). 



In this species the palisade cells are long and narrow, very 

 irregular and truncate at end. The cell cavity is very narrow 

 and extends nearly the whole length of the cell. The cavity has 

 sinuate canals which extend out from sides of the cavity. The cell 

 is colored light brown while the cavity is deeper in color. The 

 palisade cells resemble very much those of P. virginianum. The 

 sub-palisade cells, however, are much smaller with more numerous 

 indistinct layers, there being at least six layers well defined. The 

 endosperm cells also are small and quite irregular. Measurements : 

 whole seed coat, 132m ; palisade cells, 92.4m ; sub-palisade, 39.6m. 



