926 NASTURTIUM. [class xv. order ii. 



web-like 'membrane, apparently formed of a single layer of muricated 

 cells, (strikingly beautiful under a strong magnifying power), stretched 

 across a frame of condencelled cellular substance and vessels, forming 

 the placenta, from which arises the funiculi, or cords of the seeds ; 

 this frame is rigid and firm, and constantly exerting an inward 

 pressure, which the delicate septum and slender valves are unable to 

 resist when they are become dried by the sun or heat ; consequently 

 the least motion elicits the unequal pressure of the ribs upon the 

 valves, and forces them out. 



GENUS XXIX. NASTURTIUM.— Brow. Cress. 



Nat. Ord. Crucif'er^. Juss. 



Gen. Char. Siliqua nearly cylindrical, linear. Stigma sub-bilobate. 



Calyx equal at the base, spreading. Seeds small. Cotyledons 



accumbent.— (See Fig. 1, p. 871.)— Name from Nasus tortus^ a 



convulsed nose ; it is supposed to be so called from the effects of 



some of the acrid species. 



1. N. officinale^ Br. (Fig. 1071.) Water-Cress. Siliqua linear, as 



long as the pedicles; leaves pinnate, the upper ones with from three 



to seven pairs of waved sub-ovate leaflets, the lower ones with one, 



the terminal leaflet larger, roundish, or sub-cordate. 



English Flora, vol. iii. p. 193. — Hooker, British Flora, ed. 4. vol. i. 

 p. 253. — Liiidley, Synopsis, p. 23. — Sisymbrium Nasturtium^ Linn. — 

 English Botany, t. 855. 



Root of numerous long white simple fibres. Stem smooth, angular, 

 leafy, simple or branched, spreading, and mostly floating upon the 

 surface of the water, purplish at the base, very variable in length. 

 Leaves pinnate, smooth, and somewhat fleshy, a deep shining green, the 

 footstalk long, channeled, the lower ones with a pair of small lateral 

 leaflets, the upper ones with from three to seven pairs, the terminal one 

 largest, roundish, ovate, sometimes heart-shaped at the base, the 

 margins waved, or obtusely toothed. Injlorescence terminal sub- 

 corymbose racemes, much elongated when in fruit, the pedicles about 

 an inch long, slender, spreading. Calyx of four smooth oblong 

 spreading pieces. Corolla of four ovate spreading petals, with a short 

 claw. Stamens with awl-shaped ^/awewfs and yellow anthers. Fruit 

 an erect or spreading siliqua, cylindrical, about an inch long, the 

 valves turgid, smooth, crowned by the short style and obtuse cleft 

 stigma. 



Habitat. — Brooks, rivers, and springs ; frequent. 

 Perennial ; flowering in June and July. 



This is the well known Water- cress, which, from its becoming so 

 much used as a salad, is now cultivated very extensively in the neijh- 



