454 NATURAL HISTORY OF PLANTS. 
stamens and staminodes, to the form of the receptacle and its beha- 
viour after anthesis, and sometimes to the leaves and stems. The 
other variable characters are then merely used for the distinction of 
genera. The differences observed in the vegetative organs sometimes 
answer to histological modifications; but perhaps these too are only 
due to peculiarities in the mode of life, such as the parasitism of 
Cassytha. In this genus the stem does not always contain central 
spiral vessels; and the dotted vessels, mixed with the fibres in the 
wood! are surrounded by a bark of liber-cells, a cortical parenchyma 
gorged with chromule, and an epidermis sprinkled with stomates in 
linear rows.? In most of the arborescent Lauracee, on the contrary, 
it has long been noted’ that the medullary cavity of the stem is mid- 
dle-sized or large, and diminishes with variable rapidity in course of 
time; that the woody fibres are coarse and pale, intermixed with 
large porous vessels; that the young bark is often covered with len- 
ticels, and that after a certain age it presents, in the Sassafras for 
instance, longitudinal and transverse clefts. When hairs are present 
on the young epidermis they are simple and pretty rigid.“ The cor- 
tical parenchyma of the aromatic species usually contains large reser- 
voirs of essential oil, either in its periphery, or deeper towards the 
centre. These reservoirs, with yellow contents, are also found in the 
pith, which often contains numerous sclerous cells, isolated or in 
groups, and riddled with numbers of canals whose openings are some- 
times areolated. Crystals and raphides are frequently observed in 
the pith, more rarely in the bark. The liber is almost constantly 
divided into bundles isolated by alternating intrusions of the herba- 
ceous layer. 
Arrinitizs.—These easily follow from the characters above de- 
scribed, and from those of the Monimiacee related in the preceding 
volume,’ We consider that the Lauracee, whose gynzceum is con- 
stantly reduced to a single carpel, are to the Monimiacee what the 
1 Drowyz., in Ann, Sc. Nat., sér. 3, v. 247. 
2 «Thus the general aspect of a section 
through a Cassytha stem presents the strongest 
resemblance to that of a young monocotyledonous 
root” (Drcng., ke. cit.).—Cuatin (Anat. 
Comp. des Végét., ii. 27, t. 5, 6) has taken up 
the study of the histology of these stems; he 
finds trachee in but few species of Cassytha, 
having only made out their presence in C. Casua- 
ring and fil'formis. He describes the suckers 
as forming a little perforating cellular cone, 
within which is another “ reinforcing cone,” 
formed of fibres, and more rarely of vessels. 
This author concludes, differing from DrcaisneE, 
that “the habitual absence of spiral vessels in 
the stem” is the peculiar character of Cassytha. 
3 Ness, Syst. Laur., 6. 
+ Pili, si adsint, simplices,” 
Prodr,, 2.) 
5 See above, i. 822. 
(Mzissy., 
