Vegetable Physiology for the Year 1836. 527 



and to convey sap ; it is further stated to be wound round a 

 delicate tube, and to be inclosed externally by a membrane, 

 under which is the fluid; while the inner tube round which 

 the spiral fibre runs is said to convey air only. 



These are, properly speaking, the results of Girou's obser- 

 vations; he however in this memoir as well as in his preceding 

 ones never specifies the name of the plants on which he made 

 this or that observation, and on which the observation might 

 easily be repeated. He also never takes notice of the obser- 

 vations of other botanists. Towards the end of the paper Girou 

 {I. c. p. 245) comes to the conclusion, that a certain circula- 

 tion exists in plants ; the sap ascends by means of the inter- 

 cellular passages through the whole plant; it is conveyed by 

 the adducent vessels from the root to the leaves, where it 

 undergoes an elaboration, and it then passes into the vessels 

 which carry it off. The sap which is contained in the spiral 

 fibre of these vessels may descend to the root, and there in the 

 earth serve for the purpose of excretion ; but the other sap, 

 which runs between the two membranes of the downward 

 conveying vessels, is said to flow through the side apertures 

 into the intercellular passages, and there mix with the ascend- 

 ing sap. I am very sorry to say that I could convince my- 

 self of none of these positions ! 



We will examine more specially the position, that the 

 spiral fibre is hollow, for although we endeavoured many 

 years ago to show that this question was decided in a most 

 definite manner, yet many of the most learned phytotomists 

 have in these latter years contended for the presence of a ca- 

 vity in the spiral fibre ; not only Mirbel, but also Link in 

 his recent work. The latter considers it to be hollow, on ac- 

 count of some (as it appears) swollen places, as also from its 

 appearance at the points of ramification. Link*, however, 

 does not lay much stress on this opinion. 



Mohl t has also argued against the presence of a cavity in 

 the spiral fibre which Mirbel had assigned to the fibre in the 

 ringed tubes of the Oleander; he says: " If the section passes 

 exactly through the axis of the vessel, and still better, if we 

 succeed in obtaining a thin disc-like diagonal section of the 

 spiral fibre, we can very plainly observe that the spiral fibre 

 consists of two layers, as it were of a central column and of 

 a sheath. There is therefore a difference between the spiral 

 fibre and the fibres of the dotted cells ; but there is also a 

 similarity, since it is probable that the central column is 

 the first-formed part of the fibre, and the sheath a later de- 



* Elem. Philos. Bot., p. 159. f On Vegetable Substance, p. 29. 



