60 
the central axis and through the petioles of the two Coty- 
ledon leaves shew very clearly vessels arising within the 
Cotyledon passing down the petiole and after uniting with 
the central axis passing downwards along the axis towards the 
rootlets, another set of vessels appear to arise at the rootlets 
and passing upwards between the pith and a layer of cells 
which appear to separate the vessels descending from the 
Cotyledon, forms the commencement of the Medullary 
sheath. These vessels travel on to the upper portion of the 
axis from which the true leaves spring — a similar appear- 
ance is shown in sections of the French Bean stem cut 
when the Cotyledons have begun to wither away. 
The cross sections of these two plants cut through the 
central axis, below the junction of the Cotyledon (the 
Hypocotyl), shew these two rings, the descending and the 
ascending, with the separating zone of cellular tissue. The 
ascending spiral vessels are easily dyed with Aniline Green. 
The descending do not take the dye so easily, if at all. 
As growth proceeds this outer or descending zone dis- 
appears. 
