| oblong heart-shaped seeds. 
SENECILLIS. 
nursery or the garden. The word, asall Britons 
know, is also used metaphorically in the sense of 
a schoo].—the seed-bed of knowledge. 
SEMPERVIVUM. See Hovusetnex. 
SENEBIERA. See Warz-Cress. 
SENECILLIS. A small genus of ornamental 
herbaceous plants, of the jacobea division of the 
composite order. It comprises a yellow-flowered, 
annual-stemmed, hardy species, S. glauca,— 
and a purple-flowered, evergreen, slightly tender 
species, S. purpurata,—which Linneus classed 
as cinerarias. 
SENECIO. See GrounpsE. 
SHNEKA-ROOT. See Mitkworr. 
SHNNA. A well-known cathartic, consisting 
of the leaves of any one or two of several species 
of cassia. The most common senna plant is 
Cassia vtalica,—often called, by way of eminence, 
Cassia senna. This is a native of Upper Egypt, 
Nubia, and Benou ; and furnishesa large portion 
of the senna of commerce. Its root is annual, its 
stem is erect, branching, and about two feet high ; 
its leaves are pinnate, and comprise each five or 
six pairs of sessile, oval, pointed, yellowish-green 
leaflets, each scarcely an inch long, and rather 
| more than a fourth of an inch broad ; its flowers 
are produced in loose auxiliary spikes, and have 
a yellow colour, and bloom in June and July; 
and its legumes are ovate, kidney-shaped, mem- 
branous, leafy, and compressed, each having six 
or nine cells and containing the same number of 
Another senna plant 
is Cassia obovata; and this also is sometimes 
called, by way of eminence, Cassia senna. It is 
_ a native of Upper Egypt, and was introduced to 
Britain before the middle of the 17th century. 
Its root is annual; its stem is about 20 inches 
high ; and its flowers are yellow, and bloom in 
July and August. The leaves of this species are 
less purgative than those of Cassia italica, and 
constitute a considerable portion of the senna of 
commerce, but are generally mixed, even at the 
| first native market, with those of Cassia angusti- 
folia and those of Cynanchum oleifoliwm,—the 
former as good or nearly so as themselves, but 
the latter a downright adulteration—A third 
senna plant is Cassia lanceolata. This is an ever- 
| green undershruk, of about a foot in height, and 
carries yellow flowers in July and August. It is 
a native of the Levant, and was long ago cul- 
tivated in Arabia, and is now cultivated on the 
coast of Malabar. The produce of it is some- 
what extensively imported from Calcutta, and 
bears the name of Hast India senna. 
- Senna leaves emit a faint and somewhat dis- 
agreeable and sickening odour, and have a sweet- 
ish, slightly bitter, nauseous, aromatic taste. An 
infusion of them has a deep reddish brown 
colour, and possesses both their odour and their 
taste. Their active principle is a peculiar sub- 
_ stance called cathartin. See the article Carnar- 
qin. Senna is a sure and comparatively mild 
purgative; but is liable to gripe, and requires 
Rg 
to be accompanied with some aromatic. Decoe- 
tion is a bad form of preparing it; but both the 
infusion and the powder are good; and in some 
cases, the tincture, the syrup, and the electuary 
are suitable. 
SENSITIVE PLANT. Any one of several 
species of the genus mimosa,—though the name 
is most commonly given to the pink-flowered 
Brazilian biennial, J/imosa sensitiva. See the 
articles Mimosa and Irrirasruiry. “The move- 
ment of the leaves of the Mimosa pudica,” says 
Mr. C. Mackenzie, “have their origin in certain 
enlargements, situated at the articulation of the 
leaflets with the petiole, and of the petiole with 
the stem. Those only which are situated in the 
last articulation are of sufficient size to be sub- 
mitted to experiment. If, by a longitudinal 
section, the lower half of this swelling be re- 
moved, the petiole will remain depressed, having 
lost the power of elevating itself. If the superior 
half be removed, the petiole will remain con- 
stantly elevated, having lost the power of de- 
pressing itself. These facts prove that the mo- 
tions of the petiole depend on the alternate tur- 
gescence of the upper and lower half of the en- 
largement, situated at the point of articulation ; 
and that contractibility is not the principle of 
these motions. If one part of the plant be irri- 
tated, the others will soon sympathise, or bear 
witness, by the successive falling of their leaves, 
that they have successively felt the irritation. 
Thus, if a leaflet be burnt slightly by a lens, the 
interior movement which is produced will be 
propagated successively to the other leaflets of 
the leaf, and thence to the other leaves on the 
same stalk. M. Dutrochet found that this in- 
terior movement is transmitted equally well, 
either ascending or descending ; that it is equally 
well transmitted, even though a ring of bark has 
been removed; that it is transmissable, even 
though the bark and pith be removed, so that 
nothing remain to communicate between the 
two parts of the skin, except the woody fibres 
and vessels; that it is transmissable, even when 
the two parts communicate merely by a shred of 
bark; and that it may be transmitted, even 
when the communication exists by the pith only ; 
but that it is not transmissable, when the com- 
munication exists merely by the cortical paren- 
chyma. From these very interesting experi- 
ments, it results that the interior movement pro- 
duced by irritation, is propagated by the ligneous 
fibres and the vessels. The propagation is more 
rapid in the petioles than in the body of the: 
stem. In the former, it moves through a dis- 
tance of from three to six tenths of an inch ina 
second; in the latter, through from eight to 
twelve hundredths of an inch, during the same 
portion of time. External temperature does not 
‘appear to exert any influence on the rapidity of 
the movement, but very sensibly affects its ex- 
tent. Absence of light, during a certain time, 
completely destroys the irritability of the plant. 
