KNOWLEDGE OF MONOCOTYLEDONOUS SAPROPHYTES. 161 
is surrounded by a sheath of narrow parenchyma-cells longi- 
tudinally elongated. Often those in the inner side are lignified 
and stretch across from bundle to bundle within the phloém; thus 
a complete lignified ring is formed. Frequently, too, the paren- 
chyma-cells at the sides or even between the tracheides are ligni- 
fied, but heavily pitted. The tracheides are really few in number, 
and in most parts of the root the lignified portion, seen in the 
stele to form a connected mass, is mainly made up of elongated, 
heavily pitted parenchyma-cells. These in transverse section are 
easily distinguished by their protoplasmic contents. As the 
terminal walls are oblique or transverse, they might equally well 
be termed fibres. 
Phioém is mainly constituted of elongated thin-walled paren- 
chyma-cells. A few narrow sieve-tubes occur and have terminal 
sieve-plates. The sieve-tubes communicate by lateral pits with 
some of the more slender parenchyma-cells, which must function- 
ally represent companion-cells. The sieve-tubes may be recog- 
nized by their thicker glistening walls. Thus in the phloém 
there is, compared with a normal plant, an increase in the paren- 
chyma and a dwindling of the sieve-tubes. 
The pith is considerable in size, and typically consists of elon- 
gated parenchyma-cells with cellulose-walls and delicate collen- 
chymatous thickenings round the distinct intercellular spaces. 
A few longitudinal rows of raphide-mucilage cells occur. But 
at the base of the root the pith is smaller, and all its cells possess 
thick lignified walls. Travelling towards the apex of the root, this 
lignification diminishes pari passu with the lessening of the number 
of lignified layers outside the endodermis. But it is the central 
cells of the pith which first lose their thick walls, and the peripheral 
layers which preserve them longest. The number of raphide- 
mucilage cells diminishes in the pith as the lignification increases. 
Thus, at its point of attachment the root is more slender, but 
there is a large production of mechanical cells which are connected 
with similar cells in the rhizome. Examining the subterranean 
parts, one sees that some roots arise close together and exert 
considerable pressure on each other, so that there is a marked 
flattening on the side of the younger root. If there were no 
mechanical cells at the slenderest part of the root, the pressure 
of the contiguous parts would cause bending and ultimately 
rupture. Hence the advantages of a production of mechanical 
tissue at this point. I cannot say whether this production is 
