On the Formation of Rujlies, and on the StriiBure of the Nerves, 



In purfuing my obfervations on the nature of the veflels or tubes 

 of wood in trees, I turned my thoughts to the obfervation of Bul- 

 rullies. Thefe grow in great quantities in the fhallow parts of 

 our krger ftreams and rivers, and the feats or bottoms of our chairs 

 are generally made of them ; and, as they have many cavities into 

 which water will not eafily penetrate, they are ufed in time of war for 

 the making of bridges to pafs troops over fmall ftreams or canals. 



Plate XIX. fg. 33, ABCD, reprefents a piece of Bulrulh, 

 which I cut at A, in an oblique direction, that the large cavities 

 with which the infide of it is for the moft part formed, and which 

 are vifible to the naked eye, may be fecn. 



Thefe large veflels or cavities in Ruflies, are furniflied with 

 valves through their whole extent, without which the Rulhes would 

 be very brittle, and tlieir fides eafily comprefled together ; and like- 

 wife, were it not for thefe valves, if only one end of the Rufli M'as 

 laid in water, the whole would foon be filled ; but the water is by 

 thefe valves prevented entering the cavities otherwife than very 

 flowly, and the Ruflies, by reafon of the many cavities they con- 

 tain, can bear, when floating on the water, a'great weight in pro- 

 portion to their fize. 



I was alfo deflrous to fliew this cavity in the Rufli when cut 

 Icngthwife, in order to place before the eye the valves as they are 

 placed in each of thofe cavities. Fig. 33, EFGHI K, reprefents 

 a lingle velTel, with its valves forming one of the cavities of the Rufh, 

 which I fliall prefently fhevv, as it appears through the microfcope, 

 together with the nature of its formation. 



