130 On the Pki/siology of Fegetalks. 



hilt the diminut'we spirals before mentioned. Yet surely thi? 

 cOHclusion is premature, and does not follow the premises. If a 

 solid matter is taken, and a quantity of /«/-^e' holes drilled through 

 it, in its whole length.; — if that matter is capable of being taken 

 to pieces thread from thread, no vessels will appear — still no one 

 will deny that in its perfect state it was capable of receiving a 

 liquid, and passing it through these drilled passages! Such is 

 the formation of the wood : still it may be inr?i and separated 

 into the most minute threads, though certainly capable of re- 

 ceiving the sap in the many apertures and long voids formed iu 

 it for the purpose. And to prove that it does so, and that voids 

 instead of vessels are made for that purpose, a person need but 

 place a piece of wor.d in a coloured liquor, and it will taint 

 each vacancy throughout its whole length, in a manner that 

 iiiust plainly prove that the coloured liquor runs completely, 

 throiigli them. Or, if quicksilver (with the help of an air- 

 pump) is passed through the wood, it marks with black streaks 

 each projection oi' the voids: — nay, if a specimen is cut extremely 

 thin, and placed in the solar microscope, it will still more evi- 

 dently show this, by the sap running up the very passages before 

 7/our ei/es; and, if quite a fresh piece, will continue to move thus 

 tor near an hour. The passages cannot be mistaken, because 

 t!;ey may be strongly marked before they are put within the 

 glass. Nor is it difficult to und^erstand why Nature has made 

 voids in the wood instead of vessej-s. As the flower-buds pass 

 across the wood when first running to the bark, if thev had been 

 vessels they would continually have been twisted and impeded in 

 their progress, stopping the liquor they contained ; but, formed 

 as a void, they are so large as to bear being pushed a little out 

 of their places, yet not impeding the liquid (see fig. 8, gg, buds); 

 and being surrounded every half or quarter of an inch at the top 

 with the spiral wire or muscle of the plant (see fig. 1 ,ff) the 

 wood is soon again (by its own contractions) restored to its 

 usual place and parallel circle. No person can cut and place 

 a piece of the wood in the solar microscope without seeing this, 

 and without understanding the whole process. All the French 

 botanists believe as I do; that these voids are made for the sap, 

 and that the spiral wires have no passage for litiuids. Mirbel, 

 one of the best b jtanists of France, says : " *La trach(^e v^g^tale 

 e-it uu tube forme eu spirale par un filet tournt^ de droit 4; 

 gauche : ce filet est opaque, lirillant, argents, ^pais : sa coupe 



* The spiral vessels are tiihes wliich wind round a centre from right to 

 left : ihey arc perfectly opakc; and when cut across, a flat figure or ellipse 

 is (iiscovert'd, brilliant, silvery: sometimes three threads are retained by a 

 cross membrane ; but I never could perceive (says Mirbel) any opening to 

 them, in spite of the idea of some authors who are of this opinion. 



transvcrsale 



