142 



PHYSIOLOGICAL VIEWS 



parent. * These vessels extend throughout the whole plant, 

 distributing air and other fluids necessary to vegetation. The 

 vascular system of plants presents a variety as to form and 

 with respect to the functions which the different vessels 

 perform. 



Some are entire vessels, or without any perforation (Fig. 

 91, c) ; these convey the proper juices of the plant, mid are 

 generally found containing oils and resinous juices. 



Porous vessels have their sides pierced with many perfora- 

 tions (Fig. 91, b) ; they often separate and again unite, chan- 

 ging at length into cellular integument. 



Fi- 92- . Spiral vessels are 



so called from their 

 form, resembling 

 that of a screw (Fig. 

 92, a) ; they are 

 sometimes termed 

 trachea, from a sup- 

 posed analogy to the 

 trachea, or the or- 

 gans of insects for 

 breathing. These 

 vessels are formed 

 of a thread-like fibre 

 turned spirally from 

 right to left. 



Annular vessels (so called from annulus, a ring,) have per- 

 forations which make the tube appear as if composed of rings 

 (Kg. 92, b). 



Moniliform vessels (from monile, beads,) resemble, in exter- 

 nal appearance, a string of beads (Fig. 92, c) ; these serve to 

 connect large vessels, and to convey sap from one set to 

 another. 



Mosses, fungi, and lichens have no vascular system ; but 

 their vessels are all of the cellular kind. The fibres of plants 

 are all composed of some varieties of the two kinds of vessels 

 we have now described. Roots and stems are composed of 

 fibres ; these may easily be split longitudinally, as the vessels 

 in this case are only separated, and the cellular texture easily 

 yields ; but in cutting the roots and stems horizontally, greater 

 resistance is to be overcome, since the tubes are to be divided 

 or cut across. 



Vegetables, like animals, have a system of glands, or internal 

 vessels, which are by the Author of nature, made subservient 



Entire vessels, Porous vessels Spiral vessels Annular Moniliform All 

 the fibres of plants composed of some of these vessels Glands of vegetables. 



