62 CRUCIFER^E. (MUSTARD FAMILY.) 



ing a cross. Stamens 6, two of them inserted lower down and shorter 

 (rarely only 4 or 2). Pod usually 2-celled by a thin partition stretched 

 between the two marginal placentas, from which when ripe the valves 

 separate, either much longer than broad (a silique), or short (a silicic'), 

 sometimes indehiscent and nut-like (nucumentaceous), or separating across 

 into;.! -seeded joints (lomentaceous) . Seeds campylotropous, without albu- 

 men, filled by the large embryo, which is curved or folded in various 

 ways : i. e. the cotyledons decumbent, viz., their margins on one side applied 

 to the radicle, so that the cross-section of the seed appears thus o= ; or 

 else incumbent, viz., the back of one cotyledon applied to the radicle, 

 thus o||. In these cases the cotyledons are plane; but they may be 

 folded upon themselves and round the radicle, as in Mustard, where they 

 are conduplicate, thus o. In Leavenworthia alone the whole embryo 

 is straight. Leaves alternate, no stipules. Flowers in terminal racemes 

 or corymbs ; pedicels rarely bracted. A large and very natural family, 

 of pungent or acrid, but not poisonous plants. (The characters of the 

 genera are taken almost wholly from the pods and seeds ; the flowers 

 being nearly alike in all.) 



SERIES I. Pod 2-celled, regularly dehiscent by 2 valves. 



* Pod compressed parallel to the broad partition. Seeds flat or flattish, orbicular or oval ; 



cotyledons accumbent or nearly so. 

 *- Pod large, oblong-elliptical , valves nerveless. Seeds in 2 rows. Flowers yellow. 



1 . Selenia. Leaves pinnatisect. Raceme leafy-bracteate. Seeds winged. 



-- -- Pod linear; valves nerveless. Seeds in one row. Flowers yellow only in n. 2. 



2. Li eaven \vortliia. Seed winged ; embryo straight or nearly so. Annual ; stem often 



scapose, 1 - few-flowered. 



3. Dentaria. Stem naked below, 2-3-leaved. Pod coriaceous, with thick placentas, 



long-styled. Seeds wingless ; cotyledons thick, very unequal. 



4. Cardamine. Stem leafy. Pod coriaceous, with thick placentas. Seeds wingless, 



cotyledons flattened, equal. 



~ -- Pod linear, or oblong, or orbicular ; valves 1-nerved or nerveless. Seeds in 2 rows 

 (except in species of n. 5). 



6. Arabis. Pod long-linear, the flat or flattish valves more or less 1-nerved Seeds 

 winged or wingless. Flowers white to purple. Stems leafy, at least below. 



6. Draba. Pod oval to narrowly oblong or lanceolate ; valves flat or flattish, faintlv 



nerved or veined. Seeds wingless, numerous. 



7. Alyssum. Pod orbicular ; valves veinless, somewhat convex with flattened margin. 



Seeds wingless, 2-4. 



* * Pod terete or turgid, or 4-angled by the prominent midnerves. Seeds wingless, more or 



less turgid. 



(- Pods short. (See also n. 11.) 



8. L,esquerella. Pod globular-inflated, about 4-seeded ; valves nerveless. Cotyledons 



accumbent. Flowers yellow. 



9. Camelina. Pod obovoid, many-seeded valves 1-nerved , style slender. Cotyledons 



incumbent. Flowers yellow. 



10. Subularia. Pod ovoid or globular, few-seeded . valves l-nerved style none. Coty- 



ledons long, folded transversely. Flowers white. Dwarf steinless aquatic, 



