80 FARM WKKDS OF CANADA 



STINKWEED (Thlaspi arvense L.) 



Other English names: Penny Cress, French Weed, Mithridate 

 Mustard. 



Introduced from Europe. Annual and winter annual. 

 Stem erect, simple or branching. Whole plant bright green and 

 quite smooth. Root leaves borne on footstalks ; stem leaves 

 spear-shaped, coarsely toothed, clasping the stem with the arrow- 

 shaped base. Flowers clear white, 1/8 of an inch across; at first 

 in a small, flat cluster at the top of the leafy stem. Racemes 

 elongated in fruit. Pods flat, 3/4 of an inch across, containing 

 from 8 to 16 seeds, on slender, upward-curved footstalks, pale 

 green and winged, notched at the top. Just before the seeds 

 ripen the pods turn a characteristic greenish-orange shade, 

 easily noticed when this weed is growing among crops. 



The seed (Plate 73, fig. 29) is about 1/12 of an inch across, 

 a little longer than broad, deep purplish-brown, unsymmetrically 

 oval in outline, flattened, with rounded edges. The flattened 

 surface has 5 or 6 loop-like lines, which start at the basal scar 

 or notch and run concentrically around a central groove. No 

 mucilage develops on these seeds when soaked in water. 



Time of flowering : Plants in bloom when winter sets in 

 freeze up, but as soon as they thaw out in spring they continue 

 to grow and mature their seeds without the slightest injury, 

 and continue ripening until frost. The seeds of these early plants 

 are ripe early in July. Plants which grow from seed in the 

 spring are not ripe until some weeks later. After the middle 

 of June they are too far advanced to be plowed down. 



Propagation: By seeds. 



Occurrence: Stinkweed is now found in every province in 

 Canada, but nowhere else is it such a terrible pest as in the 

 Prairie Provinces, where it was introduced with the first settlors. 



