Lily-kin and Rose-kin 129 
The walls of some of these are queerly pitted, 
and those of others are beautifully marked with 
raised rings or spirals. 
When the plant is growing actively the largest 
vessels generally contain but a film of fluid cover- 
ing their walls, while the rest of the space within 
them is filled with air. 
The tubes, which are the most important part of 
the bast, have thin walls with delicate tracery, and 
are the route by which fluids descend from the 
leaves toward the roots. 
The water which a growing plant absorbs from 
the soil holds in solution many mineral and chemi- 
cal substances. This liquid-is ‘‘ crude sap,” and it 
is the material upon which three magicians work 
together. The green coloring-matter in the leaves, 
the sunlight falling upon them, and the carbon 
dioxide in the air about them, are the efficient trio. 
And the result of their subtle alchemy is 
‘« digested sap,’ which moves downward from the 
leaves into all the growing parts of the plant, 
travelling always through the bast. 
When Nature is about to make a new fibro-vas- 
cular bundle, in lily-kin or in rose-kin, a little of 
the cellular substance of the growing stem experi- 
ences a change of character, and becomes set aside, 
