TISSUES OF THE BEETROOT. 63 



in water, this section shows us more or less rectangular cells, 

 filled with a watery, colourless fluid. On the walls of these celjs 

 we notice, here and there, larger or smaller, brighter, round or 

 oval spots, which indicate shallow pits, i.e., local thin places, or 

 hollows, in the wall. In some of the cells the nucleus is visible, 

 with a distinct nucleolus, and surrounded by minute leucoplasts ; 

 also a layer of cytoplasm lining the cell-wall. The intercellular 

 spaces are usually filled with air, appearing black. In certain 

 parts of the preparation the parenchymatous cells are narrower, 

 and elongated parallel to the long axis of the root ; between them 

 are visible long tubes usually filled with air, which are distin- 

 guished by a characteristic thickening of their walls. These 

 tubes are vessels. The thickening of their walls is in a network 

 of pits (*' reticulated ") ; that is, the wall shows thickening bands 

 combined into a network, between which lie unthickened places. 

 These unthickened places, or pits, are elongated transversely to 

 the longitudinal direction of the vessels. Where the section 

 has opened a vessel, there can be seen in it, from time to time, 

 ring-like thickenings, which project into the interior of the cells. 

 These are the diaphragm-like remains of originally complete 

 partition walls, and from these remains it will be seen that the 

 vessel has proceeded from the coalescense of a row of cells. The 

 air present in the vessels often interferes with examination ; it 

 can be extracted with the air-pump. When an air-pump is not 

 at our disposal, we can endeavour to remove the air by laying 

 the preparation in freshly boiled but cold water. This is more 

 quickly done by a short immersion of the preparation in alcohol, 

 which, it is true, kills the contents of the cells, but for the fore- 

 going observation this is not of consequence. 



Here and there also in the preparation we come across isolated 

 cells, which are densely filled with small clinorhombic crystals, 

 and appear almost black. These crystals consist of oxalate of 

 lime. In order to prove this, we allow dilute acetic acid to act 

 upon them, and determine that they are insoluble in it. Into 

 another preparation we run sulphuric acid, and the crystals are 

 quickly dissolved without evolution of gas. The quantity of sul- 

 phate of lime (gypsum) formed is so small that it remains dissolved 

 in the surrounding fluid. 1 



2 Calcium Oxalate Crystals. la cases hereafter, calcium oxalate crystals 

 may be found in quantity, so that upon treatment for a few minutes with 



