140 



ANATOMY, 



above the epidermis ; they pass insensibly into each other, as ia glandular roses. The 

 superficial glands covering the bracts and flowers of the Hop (fig. 743) are simple 

 vesicles (fig. 744) containing a liquid, and a resinous principle called by chemists 

 lupuUne ; these vesicles burst and soon disappear, vyhen the resinous principle 

 remains in the form of powder. Sometimes the glands are sunk in the thickness of 

 the bark, but they are always near the epidermis ; such are the glands called vesicular 

 of the leaves of 8t. John's Wort and Myrtle, and of the bark of the Orange, which 

 contain a volatile oil (fig. 745). 



We have already described the nectariferous glands or nectaries, which secrete a 

 sweet liquid (p. 74). 



The cavities called reservoirs of proper juice, in which gums, resins, 

 elaborated and accumulated, are lined with peculiar cells ; they are 

 analogous to the vesicular glands, but more deeply immersed in the tissue. 



Lenticels, formerly called lenticular glands, are not glandular; they 



are 



743. Hop. 

 9 flower (mag.). 



744. Hop. 



Superficial glands containing 



lupuline (mag.). 



745. Orange. 



Vertical section of a fragment of rind, 



showing the 



reservoirs (R) of Tolatile oil (mag.). 



are prominences on the surface of the stem (fig. 746, 1), produced by excrescences 

 of the endopleura which have pierced the bark. Adventitious roots often spring 

 from lenticels ; but they also spring from many other points ; which invalidates the 

 opinion of De CandoUe, who regarded lenticels as the buds of aerial roots. 



ANATOMY OF ACOTTLEDONS. 



Stem. — The stems of Ferns more nearly resemble those of cotyledonous plants 

 than do those of any other acotyledonous order. A transverse section of a Tree fern 

 stem (fig. 747) shows fibro-vascular bundles (f, v) of various 

 forms, disposed in a more or less irregular circle, which 

 surrounds a yellowish central disk (m), and is itself sur- 

 rounded by a zone of the same colour (p) ; this disk and 

 zone are cellular, and communicate by larger or smaller 

 passages between the bundles. The outermost blackish 

 zone is an envelope formed subsequently to the epidermis, of 

 the bases of the fronds. A transverse section of the bases 

 of these fronds displays a structure analogous to that of the 

 stem, on which their bases, when detached, leave remarkable scars. The same 



747. Cyathea. 

 Transverse section of the stem. 



