THE CONDUCTING SYSTEM. . 213 
the anatomy of leaves, especially the epidermis and the tri- 
chomes, for the purposes of diagnosis. 
5. The Conducting System. 
When a leaf of the plantain (Plantago) is torn off or a maize 
stem is broken, there project from the fractured surface numerous 
fine threads. If the fibrous, fractured place is evenly cut with a 
sharp knife, it may be seen, even with the unaided eye, that 
there is a large number of compact, isolated dots imbedded in 
a more delicate tissue. If the maize stem is exposed to decay, 
only a bundle of very long, fibrous threads finally remains, sur- 
roundered by a delicate membrane, the cuticle. These threads, 
as is shown by an anatomical comparison, correspond to the 
dots upon the transverse section. The threads are termed 
Jibro-vascular’ bundles, vascular bundles, or conducting bundles. 
As is already evident from their considerable length, they 
serve primarly for the conduction of substances, chiefly in the 
longitudinal direction of the organ. ; 
The same extended threads we meet with in the maize leaf. 
If the latter (or any elongated leaf of a monocotyledonous. 
plant which may be chosen) is held toward the light, a large 
number of nearly parallel, lighter colored threads (nerves) may 
be seen in the green tissue. 
_ The nerves do not appear so regular in a dicotyledonous leaf. 
Here they are variously branched, anastomose with each other, 
and form a delicate network of fine lines. This is rendered 
prominent, in an especially handsome manner, when leaves like 
those of Digitalis (Fig. 130), Datura or Matico are rendered 
transparent by long maceration in alcohol (of about the specific 
gravity 0.900), or when freed by decay from the parenchymatous 
fundamental tissue * (Ettingshausen’s leaf-skeleton). 
That which applies to the leaf and stem is also applicable to 
the roots. Upon a transverse section of Rhizoma Filicis, for 
example, may be observed a double circle of such threads 
? Fibra, fibre, fibre-shaped cell, and vas, vessel. = 
*Fundamental tissue in the sense explained on page 176. 
