480 
Holden and Daniels . — Observations on the 
strands thus left continue throughout the remainder of the seedling, 
producing a root-whorl of four members and a tetrarch tap-root. 
‘ Seedling H ’ is a ‘ Type 2 ’ seedling in which the anatomy of the major 
portion of the blade shows no striking difference from its fellows (Fig. 89). 
Towards the base of the lamina, however, the midrib becomes hour-glass 
shaped in transverse section (Fig. 90), and the protoxylem, which is mesarch 
at this stage, elongates and separates into two, half supplying the adaxial 
P igs. 89-97. A ‘ Type 1 ’ seedling, showing an abnormal type of transition. 
portion of the bundle and the other half supplying the outer portion. The 
adaxial portion then separates off as a separate mesarch strand (Fig. 91) 
which soon becomes endarch, whilst the outer portion becomes exarch and 
forms a typical ‘ double ’ bundle. The endarch portion then assumes 
a slightly lateral position and is joined successively, first by two lateral 
strands (Fig. 92) from the side to which it is inclined, and then by one 
from the opposite side (Fig. 93). Finally the marginals from both flanks 
(Fig. 94) unite and together join the xylem complex previously formed, the 
