48 REPORT ON BOTANY, MDCCCXLI : 
nothing more easily seen, says the author, in the Monoco- 
tyledons with shortened internodes, than that the older vas- 
cular bundles cross (in their peripheral course) the younger 
vascular bundles, which are situated towards the outside, and 
thereby form a longer or shorter curve. This is more difficult 
to observe in the Dicotyledons generally, but is easily seen in 
some of the Mammillarias. Here is found the curved course 
of the fibres, the crossing, and, in short, every thing that has 
erroneously been considered as a peculiarity of the monoco- 
tyledonous stem. Lastly, he gives the history of the forma- 
tion of the wood. The inner cells, a small bundle of the yet 
tender cells, cease to develop themselves, and begin to form 
thickened layers by spiral deposits. The cells are extended 
in length by joining the adjacent distended cells, and fre- 
quently so much so, that the cell-membrane dries up and is 
absorbed, so that the spiral fibres frequently get into the 
intercellular spaces, as is often seen in the Gactacecc. The 
spiral fibres are subsequently converted into rings, by a 
regular and gradual distension. The cells of woody fibre 
extend themselves longitudinally, and when this extension 
no longer corresponds with the extent of the whole plant, they 
are then compelled to force themselves with their ends between 
each other, and as it were, to grow into the intercellular spaces 
of the other tissues. When the formation of cells ceases in 
the internode, it nevertheless still continues in the cambium 
in the Dicotyledons. The cells form themselves into two or 
three very unequal parts, to which a fourth is sometimes 
added. The largest inner part forms wood cells, the external 
(third if existing) remains partly parenchymatous, and partly 
forms itself into cells of the liber, whilst the walls of the cells 
of the central portion (or, if the former is wanting, the ex- 
ternal) remain quite tender and capable of propagation, and 
form the new cambium. The continued growth of the cam- 
bium is best observed in the Cactacece. Cytoblasts form 
themselves in the lowest cells of the cambium, and those small 
and tender cells grow upwards through the whole cell. Their 
contiguity to the next upper wall occasions the same process 
of growth, and thus it continues. The spiral-formed layers 
440 
