THE ANATOMY OF STEMS. 253 



The holloiv or fistular monocotyledonous stems are 

 composed of distinct portions, united by knots ; at each 

 of which the cavity is divided by a diaphragm ; or 

 rather, each portion may be regarded as a distinct in- 

 dividual, which takes its origin from one knot, and ter- 

 minates in another, out of which again a new indivi- 

 dual arises, and so on in succession. The general 

 structure of this description of stems is best exempli- 

 fied in the Grasses. Thus, in Wheat we perceive the 

 upper articulation rising within the knot, in which the 

 lower has terminated ; with the leaf which infolds it 

 crowning the embracing knot. The organization of 

 this kind of stem cannot be readily distinguished with- 

 out the aid of the microscope. It is seen, in a longi- 

 tudinal section, to consist of several layers of narrow 

 oblong cells, which constitute its exterior and more 

 solid part ; and of an interior more open cellular sub- 

 stance, enclosing vascular, ligneous cords, composed 

 of oblong cells like those on the circumference, sur- 

 rounding spiral and annular vessels. In the transverse 

 section, the divided extremities of these cords appear 

 as clustered vascular spots in the cellular substance. 



The bark, if the surface of the stem can be so call- 

 ed, of the more solid monocotyledones, is formed of 

 the footstalks of the leaves ; but the real epidermis of 

 both the ligneous and herbaceous stems of this tribe, 

 is always, as has been already stated, so closely ap- 

 plied to the part which it covers, as to be inseparable 

 from it by any means. Owing to this circumstance 

 it appears of a cellular texture, and its character is 

 regulated by the nature of the parts it immediately 

 encloses. In those plants in which it can be readily 

 examined, it displays, under the microscope, a regu- 

 lar series of organic exhaling pores, each apparently 

 surrounded by a glandular border ; as is well demon 

 strated in culm of the Wheat : but in some plants, as, 



