i:\AMINATION. 79 



CHARLOCK, WILD MUSTARD. 



Brassica arvensin (L.) B. S. I*. 



This weed is a frequent contamination of grains, and to a casual 

 observer the entire seed looks like black mustard seed, though a 

 comparison will si low the charlock to be slightly larger, plumper, and 

 usually of darker color. 



When ground, (lie seed coats show the characteristic palisade cells 

 common to the Brassica family. (Plate I, fig. 1.) A distinguishing 

 test , however, has been observed in its reaction toward chloral hydrate 

 solution. When boiled with this reagent, as is done in clearing for 

 microscopical examination, a deep crimson color is developed, which 

 has not been noted for other species of this genus. 



COMMON PIGWEED. 



Chenopodium sp. 



The seeds of the two common species are much alike in size and 

 shape, the O. album~L. being possibly a little the smaller. To the akene, 

 as commonly found, more or less of the dried floral envelope is 

 attached. The seeds are nearly in the form of biconvex lenses and 

 have a diameter of to 1J nun. Those of C. album L. have a some- 

 what glossy surface while those of C. murale L. have a dull surface. 



In color and resistance to clearing, the seed coats of this species 

 resemble strongly those of rough 'pigweed. A microscopic exami- 

 nation reveals a surface composed of cells more or less rectangular or 

 rounded in outline and of about 30 j* to 75 yw in longest diameter, 

 with somewhat rounded corners. (Plate I, fig. 5.) The surfaces of the 

 cells are covered with papilla-like projections, giving a dotted or 

 punctate appearance. 



ROUGH PIGWEED. 



Amaranthus sp. 



The seeds of A. blitoides S. Wats., A. hybridus L., A. retro- 

 flexus L., and A. albus L. are flattened seeds with a very glossy 

 black surface (brown in seeds not perfectly ripe). In size the A. 

 blitoides is the largest, being about 1 to 1J mm in diameter; A. albus 

 is the smallest, about J mm. The seeds of A. hybridus vary in 

 size from to 1 mm, and are slightly elongated into ovate form. 

 The same may be said of A. retrojlexus, though in size the seeds are 

 intermediate between A. hybridus and A. albus. 



The coats of this seed are dark brown in color and when cleared 

 sufficiently are found to present in surface view a mosaic work. of 

 polygonal cells of approximately six sides. The cells are of about 

 17 // to 35 /* in diameter. (Plate I, fig. 6.) The limits of the cells 

 are defined by a sharp, fine line. The surface of the cells are covered 

 thickly by fine dots, giving almost a punctate appearance. 



