SOLID PAKTS OF VEGETABLES. 
103 
pulpy and fleshy fruits, and the stems of grasses ; consti- 
tutes the principle part of mushrooms and other cryptogamous 
plants. In the bark of plants it is situated under the cuticle, 
l^iving its color to the bark, as the same texture under the 
'luman cuticle does to the skin. In the pith of young plants 
'Jie cells are filled with watery fluids, but in older plants they 
are empty, or only filled with air. 
118. V^asGula/r or vegetable fiber consists of membraneous 
tubes tapering to a point at each end; they unite by fre- 
quent anastomoses^ and thus form a kind of net-work; they 
are protected by a coating of cellular integument ; their sides 
are thick and almost opake. They extend throughout the 
whole plant, distributing air and other fluids necessary to 
vegetation. The vascular system of plants presents a va- 
riety in respect to form, and the functions which the difler- 
ent parts perform. Entire vessels exist without any perfora- 
tion ; these convey the proper juices of the plant, and gen- 
erally contain oils and resinous juices. Porous vessels ex- 
hibit many perforations ; they often separate and again unite, 
changing at length into cellular integument. Bjpircd^ or screw 
form vessels (Fig. 124, d)^ 
are also called in^achecB^ 
from a supposed analogy 
to the tracheae or breath- 
ing organs of insects ; they 
appear to the naked eye 
like silvery threads, fine 
as a spider's web. By 
pulling asunder carefully 
the young stems or leaves 
of some plants, we may 
see these shining fibers 
still extending from one 
severed portion to the 
other. They are so elastic that they may be somewhat drawn 
out, and will coil themselves into a bundle when the exter- 
nal force ceases to act. The fiber turns spirally from right 
to left. Ducts {ov false traohecB) are vessels in which the inter- 
nal fiber does not form a complete spiral coil ; they may be 
annular (Fig. 124, J), the sides being marked with transverse 
coils or rings. Moniliform ducts (from monile^ a necklace) 
have a beaded appearance formed by porous cells contracted 
at their point of union (Fig. 124, c) ; these serve to connect 
larger vessels, and to convey sap from one set to another. Lac- 
tiferous (or milk) vessels are met with in the inner bark and 
lis Vascular fiber— Entire vessels — Porous — Soiral- -Ducts— Moniliform— Laetiferon*. 
