90 PLANT ORGANS OR PARTS OF PLANTS. 



cotyledons little or no change takes place in the roots, 

 but in gymnosperms and dicotyledons a series of changes 

 take place which modify both cortex and central cylinder. 



In the cortex the cells of the epidermis become de- 

 tached and new tissues grow in order to make the outside 

 correspond with the internal growth. A layer of meris- 

 tematic tissue, the Phellogen, becomes active, and new 

 secondary cortical tissues are formed on the inside and a 

 bark is made on the outside of this layer of growing cells. 

 The bark of roots and stems differs somewhat ; this will 

 be touched upon under the subject of barks. Inside the 

 endodermis, a structure which may disappear, a still 

 greater change is taking place in the development of the 

 fibro- vascular bundles. These commence to approximate, 

 new meristematic tissues develop in their interfascicular 

 cambium, the cambium itself becomes more prominent, 

 forming cell groups just inside the pericycle and ex- 

 tending to the bast groups. This, the fascicular cam- 

 bium, and the cambium which develops between the 

 bundles, the interfascicular cambium, soon join to form 

 a continuous circle, and the cambium ring of dicotyledons 

 and many gymnosperms is thus formed. By means of this 

 cambium new structures are added to the xylem internally 

 and to the phloem externally. The structures of the 

 xylem of the secondary growth are similar in some respects 

 to those of the primary growth, and yet in certain other 

 features they differ; thus there are no spiral vessels 

 formed, as a rule, in the secondary xylem, woody paren- 

 chyma is commonly formed and the tracheal elements are 

 found. 



SARSAPARILLA. 



Sarsaparilla is the root of Smilax ofjicinalis, Kunth., 

 Smilax medica, Smilax papyracea, and of other (unde- 

 termined) species of Smilax (nat. ord. LiliacecB). 



The main types in the United States markets are the 

 Jamaica, Honduras, Mexican, and Para sarsaparillas ; 



