78 Prof. C. Morren on the discoid Piths of Plants, 



to be thus separated, laid flat one upon another in horizontal 

 planes. 



We have seen that the slits do not extend to the circum- 

 ference of the pith. There in fact the prismatic cells are no 

 longer elongated, but as broad as they are high {d, fig. 4.). 

 Nearer the exterior also the cells are again elongated, but in an 

 inverse direction; there they are perpendicular, that is to say 

 parallel to the hgneous vessels on one side and to the axis of 

 the stem on the other {b, c, fig. 4.). At the same time they 

 become narrower, and it is these which represent the pith it- 

 self in very old branches ; they are never divided by horizon- 

 tal slits ; their longitudinal elongation is opposed to this. 



But what is most curious is the change which takes place 

 in the contents of these cells, whether they be taken in the 

 slit parts or in the circumference of the pith. In the cells 

 longitudinally elongated and in those which are of equal dia- 

 meter in every direction there is a great agglomeration of 

 grains offecule [d, d, fig. 4.). These granules are spheroidal, 

 w^hite, and vary greatly in diameter. More towards the 

 centre some cells show these feculaceous grains, smaller and 

 less frequent, and here and there octohedral crystals [f, fig. 4.) ; 

 in the sht pith we see, though but seldom, cells with a nu- 

 cleus en couronne [g, fig. 4.), but most frequently the cell is 

 destitute of any internal body with the exception of its water 

 of vegetation, which is transparent, without globules, and 

 fills all its cavities, rendering them true aquiferous vessels. 

 Such is the composition of this pith in its early stage. 



Now let us take an old stalk of Begonia argyrostigma. Here 

 things have taken quite a different aspect. A derm which 

 has become brown («, fig. 3), a cellular envelope solidified by a 

 ligneous deposition [b, fig. 3.), a system of white wood (c, fig. 3.) 

 clearly distinct from the nodal, ligneous and very hard dia- 

 phragms {d, fig. 3.), and a pith singularly formed of exceed- 

 ingly numerous, transverse, very thin discs, leaving between 

 them lenticular cavities (/, fig. 3.), but generally formed by 

 two discs with separate roots, discs which join at their 

 centre, so that their double roots leave a fresh space empty 

 between them [g, fig. 3-). It is just as if the pith had slit or 



