LECT. III.] VASCULAR TEXTURE. 85 



Willdenow and others have asserted, that it is 

 hollow, and forms a real vessel thus twisted in a 

 spiral manner; or, that the larger hollow tube 

 is an air-vessel, while the spirally twisted thread 

 is a vessel carrying fluid. For, if we consider the 

 smallness of the larger tube, and the flattened state 

 of the thread of which it is formed, the impos- 

 sibility of any fluid entering the smaller one, if it 

 really existed as a vessel, may be easily conceived. 

 According to Hedwig's observations, made with a 

 microscope which magnified 290 times, he found 

 that the apparent diameter of these air-vessels, as 

 he supposes them to be, is one tenth of an inch ; 

 their real diameter must, therefore, be the 

 290th part of the tenth of an inch, or the 2,900th 

 part of an inch. What then, I 

 would ask, must the diameter of the 

 supposed spiral vessel be, and what 

 fluid could be conducted through it ? 

 The thread is sometimes double 

 (fig. k) ; and Mirbel asserts, that 

 it is furnished with a glandular 

 border (fig. /). 



These vessels are found in 

 great numbers in monocotyledonous 

 plants *, as in the centre of the ligneous threads 



* These are plants, the x seeds of which have one lobe only ; 

 the term monocotyledon being a compound of the Greek word 

 /*ooj (monos), one, and x.o->v\v$uv (kotuledon), hollo\v. 



G 3 



