68 FABRIC OF PLANTS. 



fifty times finer than a horse hair, forming a larger 

 tube, as if we should suppose a walking cane composed 

 of small straws, as in the following figure. 



Leuwenhoeck describes them as composed, like the 

 quills of birds, of two transparent tissues, one placed 

 lengthways, and the other across, with no lateral 

 communication. 



Hill tells us that some of these vessels collapse 

 when emptied of their contents; and though he 

 fancied he had discovered cells in them, these turned 

 out to be only globules of fluid. He says they 

 communicate with the cellular tissue by minute 

 mouths. 



M. Mirbel, reverting, as it should seem, to the 

 opinion of Malpighi, describes all the vessels of what- 

 ever form, as cells variously developed, with pores in 

 their sides ; a fanciful notion which he exults over as 

 original. 



Pores of Tissue. 



As to the existence of pores or openings in_ the 

 sides of those vessels, Malpighi supposed them to be 

 only irn perforate elevations. 



