ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
363 
the Crucifer® varies from species to species. Black mustard contains 
sinigrin besides the ferment myrosin, as also does the horse-radish ; 
while white mustard contains sinalbin in place of sinigrin. The 
active principle of Cochlearia officinalis is isosulphocyanate of secondary 
butyric alcohol ; while the root, the stem, and the seed of Sisymbrium 
Alliaria and Thlaspi arvense contain a mixture of sulphur and sulpho- 
cyanate of allyl. The following are the author’s conclusions on his 
researches : — (1) Nearly all the Crucifer® are provided with special 
cells which contain a particular ferment, myrosin. It is in the seed 
that these cells occur most abundantly. (2) When these cells arc 
found in the root it is in either the cortical parenchyme or the 
parenchyme of the liber ; in the stem it is generally in the pericycle ; 
in the leaf in the pericycle of the foliar bundles ; in the cotyledons 
the localization is the same as in the leaf. (3) These special cells can 
be immediately distinguished by the nature of their contents. Pure 
hydrochloric acid, under the influence of heat, gives them a violet 
coloration. (4) In the embryo these specialized cells are differen- 
tiated some time before the maturity of the seed. (5) Sometimes in 
certain seeds ( Lunaria , &c.) the embryo is rich in the glucoside, while 
the ferment is contained almost exclusively in the integument. (6) The 
ferment appears to be identical in all members of the family. (7) The 
presence or absence of the specialized ferment-cells can be made use of 
for purposes of classification. 
C3) Structure of Tissues. 
Vascular System of Floral Organs.* — Rev. G. Henslow describes 
and figures the course of the vascular cords in the various parts of 
the flower in 34 different natural orders. No appreciable differences 
are to be detected between the cords or traces of a sepal, a petal, a 
stamen, or a carpel. They all consist of the same two elements — spiral 
vessels or tracheae representing xylem, and sieve-tubes or soft bast 
constituting the phloem. The predominating arrangement in all the 
floral structures is for the spiral vessels to be either placed accurately in 
the centre of a cylinder of phloem or to be scattered irregularly through 
it. In the pedicel the arrangement of the cords characteristic re- 
spectively of the stem of Exogens and Endogens is frequently reversed. 
The system of cords formed in the wall of the ovary of the poppy, 
alternating with the placentas, originates quite freely from meristematic 
tissue imbedded in the parenchyme, and has no connection with any 
cords arising from the axis. 
Pericycle and Peridesm.f — In astelic stems (i. e. without any central 
vascular cylinder) M. P. Van Tieghem proposes to designate the layer of 
cells or the tissue which, beneath the special endoderm, surrounds the 
phloem and xylem of each vascular bundle, the peridesm , instead of, 
as hitherto, the special pericycle. Where the astelic stem is also 
“ dialydesmic,” as in the Nymphaeacese, some species of Ranunculus, 
Ophioglossum, and some species of Equisetum , the peridesms are indepen- 
dent, as are the vascular bundles ; but when the stem is “ gamodesmic,” 
* Journ. Linn. Soc. (Bot.), xxviii. (1890) pp. 151-97 (10 pis.). 
t Journ. de Bot. (Morot), iv. (1890) pp. 433-5. 
