78 VASCULAR TEXTURE. [LECT. III. 



their structure can be obtained only by means of 

 powerful microscopes. 



Notwithstanding these facts, the existence of 

 a vascular system in plants has been altogether 

 doubted ; and the subject has given rise to much 

 controversial discussion. I might amuse you by a 

 detail of the opinions delivered on both sides of 

 the question ; but little would be gained by such 

 a display ; and it will be much more satisfactory 

 to you, to direct your attention to those facts only, 

 which have been clearly demonstrated and which 

 are generally admitted as correct. , 



The Botanists to whom we are chiefly indebted 

 for the information we possess relative to the vege- 

 table vessels, are Mirbel and Mr. Knight. The 

 former examined them by means of microscopes 

 of great power, and developed their real structure ; 

 the latter made many experiments on them by 

 means of coloured fluids, which have thrown the 

 greatest light on the vegetable physiology. Let us, 

 therefore, take these two celebrated Phytologists as 

 our guides in this part of our inquiries. 



The Vascular or tubular portion of the vege- 

 table structure composes a kind of net-work, 

 owing to the frequent communication or anasto- 

 mosis of the vessels with one another, which per- 

 vades almost every part of the plant. The parti- 

 cular vessels vary both in form and in the diameter 



