160 CONSERVATIVE ORGANS. [LECT. IV. 



section shows them like coloured points, set in a 

 diamond form, in the white parenchyma (Ib. fig. 2). 

 In the old tuber this appearance varies ; the lon- 

 gitudinal section showing the cords of vessels sur- 

 rounded with the cells still turgid with fluids to a 

 certain distance on every side, and these enclosed 

 as it were with a wall of empty cells, which in a 

 transverse section assumes a circular or irregular 

 hexagonal figure ; or each cord of vessels appears 

 as a point in the centre of a large circle or 

 hexagon, the interior of which consists of moist 

 cellular matter, and the walls of dry or empty 

 cells (Ib. fig. 3). This appearance of the old tuber 

 can be explained only on the supposition that 

 during the exhaustion of the nutritious matter it 

 contains, the fluids pass laterally through the cells 

 towards each cord of vessels, by which they are 

 taken up and conveyed to the vessels of the stem 

 and those of the new tuber ; and consequently, 

 the more distant cells being those soonest emptied, 

 and each cord of vessels acting as the attractive 

 centre of a given space, the cells on the periphery 

 of each space, owing to the positions of the vas- 

 cular cords, must necessarily be emptied in such 

 a manner as to give the circular or hexagonal ap- 

 pearance to the transverse section. If this opinion 

 be well founded, it would appear, that the vessels 

 of the tubers of monocotyledonous plants, which 

 during the growth of the tuber convey to and 



