J acks on. —Anatomical Structure of the Roots of*' Bar ley. 31 
approximate more and more to the branched type. At the same time the 
internal anatomy undergoes certain changes. Fig. 10 represents a section 
of a root of this transition type. The most noticeable feature is the 
increased development of thickened cells in the central tissue of the stele. 
The endodermis is also thickened, though not to such a great extent as in 
the typical branched root. The only cells which are still thin-walled are 
those of the pericycle and those between the several xylem groups. The 
phloem cells also become more differentiated and assume the appearance of 
the corresponding tissue in the branched roots. 
part of aTS.ofa 
Transition root. 
(taken near grain) f 218) 
piliferous layer, 
cortex. 
endodermis. 
pericycle. 
protoxy/em. 
phloem, 
xylem vessel. 
sderised pith, 
centra! duct. 
Fig. 10. 
The question then arises as to what happens to the newly formed parts 
of these transitional roots. Fig. 11 is drawn from a section taken near the 
tip of a root, which was obviously of the ‘ unbranched ’ type but carried 
a number of laterals. A section near the grain of this root shows essentially 
the same structure as that of Fig. 10, that is, there are five large central 
ducts and a considerable number of thickened cells in the stele, but here at 
the tip there are only two very large central ducts and the development of 
thickened tissue is still more marked. The phloem is also well differentiated 
and the pericycle and endodermis are thickened, especially in the zones 
between the xylem groups. In the water-culture material several roots 
