ANATOMY OF PLANTS. 181 



itself; (Kieser Mem. Tab. IX. Fig. 40.; Tab. XIV. Fig. 

 67.) 



But it is characteristic of these punctured vessels, that they 

 are always larger in their diameter than the primitive spiral 

 vessels or the vasa scalaria, so that in many kinds of wood, 

 particularly in the Bamboo, and the common chair cane, wc 

 can see their sections with the naked eye. But not unfrc- 

 quently the pores of the sides are so regular, and the bladder- 

 form of this canal is so surprising, that we might be disposed 

 to suspect a transition to the porous cell-form, especially as 

 in our Pines, the latter varies so much, that, besides the 

 pores, spiral windings also appear, as in the Yew and the 

 Larch ; (Kieser''s Grundzuge der Anatomie der Pflanzen, 

 Tab. V. Fig. 47. and 48.) 



284. 



As, then, the spiral vessels, and all their varieties, are 

 uniformly found empty of fluids ; as they shew themselves 

 only in the higher plants, and constantly appear wherever a 

 strong shoot is sent out ; as they are always in the com- 

 pany of the sap- vessels ; as, in fine, they maintain, by their 

 constant diagonal direction, the middle situation between 

 the perpendicular and the horizontal ; — from all these con- 

 siderations we must suspect that they are the instruments of 

 the higher vital activity of plants, and that they are the or- 

 gans by which the sap-tubes suffer an external excitement to 

 the speedy propulsion of the sap. 



II. Ofi the Structure of Roots. 



285. 

 The internal structure of the individual parts of plants is 

 always composed of the three primitive forms which we have 

 now described. With respect to roots, in particular, they 

 consist, as was formerly (64.) stated, of the radix and radicle. 

 The latter, as being the organ appropriated to the absorption 

 of the sap, is furnished, for this purpose, in perfect plants. 



