586 Holden and Bexon.—On the Seedling 
limit of differentiation, but this seedling is too young to determine the effect 
of the persistence of the phloem groups on the root structure. 
Seedling C. This is an older seedling of the same type as seedling A, 
the phloem of one of the plumular midribs persisting throughout the hypo- 
cotyl and below the collet, though subsequently dying out. Preparation for 
the formation of the intercotyledonary root poles is evident below the collet, 
small xylem elements appearing associated with the adjacent margins of the 
lateral metaxylem groups. These are separated at first by the intrusive 
plumular phloem, but approach each other after this has disappeared. 
Seedling D. This is similar in type to seedling C, except that the phloems 
of both plumular midribs are persistent to the limits of differentiation. 
Seedling E also resembles seedling C, but in this case the persistent 
plumular strand consists of both xylem and phloem, a small collateral vas¬ 
cular strand appearing therefore in the intercotyledonary plane throughout 
the hypocotyl. As in the seedlings previously described, small xylem 
elements appear on either side of the persistent bundle in preparation for the 
formation of the intercotyledonary root pole, the xylem of the bundle bifur¬ 
cating, and the halves moving towards these small elements. Meanwhile, 
a group of phloem has appeared on the other side of the axis and small 
xylem elements are differentiated on either side of this second ploem also. 
At the limit of differentiation these arrangements still prevail, but the phloem 
group which was last to appear is becoming much reduced in size and seems 
about to disappear. 
Group 2. 
Seedling F. In this seedling normal structure obtains throughout the 
hypocotyl and the upper part of the root. When the organization of typical 
root structure is almost completed, however, a group of metaxylem appears 
lying inside the phloem between a cotyledonary and an intercotyledonary 
pole. This does not cause any disturbance of root symmetry, and in the 
lowest sections is approaching the adjacent cotyledonary pole. 
Seedling G is obviously of the same type as seedling F f and like it 
shows normal structure in the hypocotyl and upper part of the root. At 
this stage, however, a fifth xylem group appears within one of the four 
phloem groups. The phloem bifurcates and a fifth root pole is established, 
this being followed at a slightly lower level by a sixth pole developed as the 
result of the intrusion of a new xylem group directly opposite the fifth. 
Hexarchy prevails throughout the remaining part of the root. 
Seedling H, though showing distinct affinities with the two seedlings of 
Group 2, has additional peculiarities of considerable interest. The behaviour 
of the epicotyledonary strands is normal, as is that of the cotyledonary 
strands, except that the central isolated protoxylems die out. One appears 
again sporadically as one or two small elements throughout the hypocotyl 
