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 nsed 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 1 are surrounded by a bark of liber-cells, a cortical parenchyma 

 gorged with chromule, and an epidermis sprinkled with stomates in 

 linear rows. 2 In most of the arborescent Lauracea, on the contrary, 

 it has long been noted 3 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. 4 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. 



Affinities. — These easily follow from the characters above de- 

 scribed, and from those of the Monimiacea related in the preceding 

 volume. 5 We consider that the Lauracece, whose gynseceum is con- 

 stantly reduced to a single carpel, arc to the Moniudaccai what the 



DrCNE., in Ann. Sc. Nat., ser. 3, v. 247. as forming a little perforating cellular cone, 



"Thus the general aspect of a section within which is another "reinforcing cone," 



through a Cassytha stem presents the strongest formed of tihres, and more rarely of vessels. 



resemblance to that of a young monocotyledonous This author concludes, differing from Decaisne, 



root" (Decne., Ice. cit.).— Chatim (Anat. that " the habitual absence of spiral vessels in 



Comp. des Veget, n. 27, t. 5, 6) has taken up the stem" is the peculiar character of Cassytha. 



the study of the histology of these stems ; he 3 Nees, Sgst. Lour., 6. 



finds tracheae in but few species of Cassytha, * " 1'ili, si adsint, simplices." (Mbibsk., 



having only made out their presence in C. Castia- Prodr., 2.) 



rina and filiformis. He describes the suckers 5 See above, i. 322. 



