Syncotyly and Schizocotyly . 8 1 1 
the same time the corresponding protoxylem divides : the phloem branch 
coming to lie between the two half-protoxylems. A radial division then 
occurs along the cotyledonary plane on this side, separating the median 
xylem and phloem into two halves and thus producing two triads which 
enter the split cotyledon (cf. Cannabis , Figs. 27, 28). The other undivided 
polar protoxylem serves the unsplit cotyledon. 
Thus the chief differences from Cannabis are (i) the mode of origin 
of the new phloem group by a branch instead of de novo (but cf. Cannabis , 
Seedling D) ; (ii) the high level at which the xylem forks. 
Phacelia tanacetifolia (Hydrophyllaceae). 
Abundant schizocotyls were obtained from Professor de Vries’s seed : 
his £ intermediate race’ yielding an average of 57 % of schizocotyls. 1 
Dicotyls. The root is diarch, with a continuous one to two-seriate xylem- 
plate. In this slender seedling the transition is a high one, the cotyledon 
xylem-trace being widely V-shaped at the node, with two phloem groups on 
its flanks ; shortly after entering the lamina the phloems fuse dorsally, and the 
midrib branches. No exceptional features worth recording were observed. 
Schizocotyls. 
Hemitricotyl A. The structure was diarch throughout the hypocotyl 
and in transition ; after entering the deeply-split cotyledon the ‘ double 
bundle ’ began to divide equally, each half taking one of the two phloems 
and passing into the cotyledon lobe. 
Tricotyl B. The root was diarch. About a quarter up the hypocotyl a 
new detached protoxylem appeared, dividing the adjacent phloem into two 
groups : this new xylem gradually increased in size, and joined on to 
the original diarch xylem-plate half-way up the hypocotyl. Thus a triarch 
‘root-like’ structure was produced. Towards the cotyledonary node the 
three xylems developed into double bundles, one of which entered each of 
the three sub-similar seed-leaves. 
This ‘ diarch-triarch ’ structure is common in tricotyls : there being 
much variety, however, in the level at which the new protoxylem appears. 
This method of increase in the number of protoxylems is the one generally 
adopted in Phacelia: Hemitricotyl A being the only instance observed 
of radial division such as is typical of Cannabis sativa. It is the method 
followed by the vascular bundles of so-called ‘ subsidiary cotyledons ’ in 
Coniferae. 2 
Tricotyl C. The whole seedling was constructed on the triarch plan, 
from root-tip upwards. The behaviour of the vascular system was strictly 
analogous with that of the dicotyl. Trimery continues in the epicotyl also. 
This symmetrical type of structure is frequent, though perhaps not 
quite so abundant as varieties of the type of Tricotyl B. In seedlings which 
1 de Vries (’ll), p. 436. 2 T. G. Hill and de Fraine (’ 08 ), p. 708, &c. 
