406 Mr. Bowman on the Parasitical Connection 



forming a confused mass under the point in contact with the 

 fibre. By this system of vessels the food of the parasite is 

 doubtless alienated and conveyed along the root-like fibres into 

 its subterranean stem ; and from their dispersed and sinuous 

 course within the tuber, it is probable the sap may there undergo 

 a necessary change. These vessels consist of a close series of 

 minute semi-opake oval bodies, and have a moniliform or beaded 

 structure. Tab. XXIII. Fig. 3. shows a transverse section of 

 a tuber and its central vessels. 



Some of the many tubers I examined, differed materially from 

 the rest, and deserve attention, from the light they appear to throw 

 upon the nature of the action excited by parasites in general. 

 The section Tab. XXIII. Fig. 4. is one of these ; it is divided in 

 the direction of the fibre and of the vessels of the Ash root on 

 which I found it. The interior of the tuber was more densely and 

 uniformly cellular than usual ; and instead of the meandering 

 group of beaded ducts in the centre, it had on each side, near its 

 circumference, a separate set of anastomozing vessels, strong and 

 darker coloured near their contact with the fibre, but becoming 

 gradually paler and more delicate as they approached the middle 

 and lower portions of the tuber. Each fascicle communicated 

 with the fibre by a single detached trunk, and the spaces be- 

 tween a few of the larger reticulations only, were transparent ; 

 the remainder of the section being much more opake. than in 

 Tab. XXIII. Flo;. 1. & 2. Here also was no trace of the 

 funnel-shaped process ; and the only symptom of derangement 

 or disease in the bark and alburnum of the Ash root, was a 

 number of small globules, mostly detached, but more closely 

 congregated beneath the centre of the tuber. Both the funnel 

 and dark anastomozing vessels just described, were wanting in 

 other tubers ; but they contained the transparent globules, which 

 were also seen more perfectly formed in the alburnum under- 

 neath. 



