536 



WEED FLORA OF IOWA 



RANUNCULACEAE, CROWFOOT FAMILY. 



Common Buttercup {Ranunculus abortivus L.). 



The greenish achenes of the buttercup consist of three distinct 

 layers. The outer epidermal is of elongated, thickish black cells. 

 The cells containing the brown pigment are yellowish brown. 

 The underlying layers of three or four rows of seeds are similar 

 but larger and paler in color. This layer is followed by a thick- 

 walled sclerotic layer containing three or four layers of thick- 

 walled cells with pore canals. The testa consists of an outer layer 

 of thin-walled parenchyma cells ; the inner layer consisting of 

 sclerotic parenchyma cells filled with pore canals. The endosperm 

 cells are large or thin-walled and contain protein material. Harz 

 has given an account of the structure of R. arvensis*. 



Fig. 413. Microscopic structure of the seed of Buttercup (Ranunculus aborti- 

 vus). 

 ep=epi<3ermis. p=parenchyma. scl=sclerotic parenchyma. en=endosperm. 

 (Drawing by L. H. Pammel and Charlotte M. King.) 



PAPAVERACEAE, POPPY FAMILY. 



Common Poppy (Papaver somniferum L.). 



Prof. A. L. Winton describes the seeds of this plant as follows : 



Testa (S). — Cross sections are prepared after soaking the seed 



in water that may be cleared with chloral or alkali. After soaking 



the whole seed for about twenty-four hours in 1 per cent sodium 



hydrate solution, the first four layers readily separate from the 



*Landw. Samekunde 2 :10-64. 



