SPECIES AND VARIETIES. 47 



(17) Teesdalia. 



T. nudicaulis : annual, dwarf; leaves radical, pinnate, with 

 a larger terminal lobe; flower-stems leafless, bearing very 

 small white flowers. — Dry gravelly places. Fl. May. 



(18) Thlaspi. Penny-cress. 



T. arvense : annual ; stem erect ; leaves oblong, toothed ; 

 flowers small, white. — Mithridate Mustard. — Waste and cul- 

 tivated ground. Fl. May to July. 



T. perfoliatum : annual ; stem erect ; root-leaves ovate or 

 orbicular, upper ones oblong, stem- clasping; flowers small, 

 white. — Limestone pastures, rare. Fl. April, May. 



19. Viola. Violet. 



* Stem very short, the flowers and leaves appearing to grow 

 from the root. 



V. palustris : leaves kidney-shaped, smooth ; flowers pale 

 blue, with purple streaks, scentless. — Marshy places. Fl. April. 



V. odorata : leaves heart-shaped, downy or shortly hairy ; 

 flowers bluish-purple or white, rarely purple reddish or lilac, 

 sweet-scented. — Hedge-banks and thickets. Fl. March, April. 



V. hirta: leaves heart-shaped, rough with hairs; flowers 

 pale blue, scentless. — Limestone woods and pastures. Fl. 

 April, May. 



** Stem elongated, evident. 



v. canina : primary stem short, flowering branches elongated 

 ascending or erect; leaves ovate-cordate; flowers large, pale 

 blue, scentless. There are several varieties. — Hedges, groves, 

 and thickets. Fl. April to July. 



V. tricolor : biennial or perennial ; stem branching ; leaves 



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