795 
Syncotyly and Schizocotyly . 
examine other species with more complex vascular anatomy we find that 
fusion of cotyledons has led to reduction in the total vascular system of the 
seed-leaves, this being so pronounced in the more advanced cases of 
syncotyly as to affect the hypocotyl and root. 
HELIANTHUS ANNUUS (Compositae). 
The material examined was grown from seeds, provided by Professor 
H. de Vries, of a strain which produced from 50 to 95 % of more or less 
syncotylous seedlings. 1 
The seedlings showed a great range of variation from normal dicotyls 
to syncotyls with completely fused cotyledons and to amphisyncotyls. The 
syncotylous seedlings were all more or less dwarfed and grew irregularly, 
the plumule having much difficulty in developing. 
The vascular anatomy showed a corresponding range of variation, and 
several examples must be described. 
Dicotyls. The anatomy of very young seedlings has been described by 
Chauveaud. 2 The older stages of development were studied by Reinke, 3 
whose description the present author is able to confirm. For the sake of 
convenience and completeness the dicotylous structure will here be described, 
especially as certain new points can be included. 
The root is tetrarch, there being a solid four-rayed xylem star 
without pith, and four phloem groups alternating with the protoxylems. 
The xylem is usually somewhat irregular, owing to the abundance of lateral 
roots (Fig. 3). The transition changes begin at a low level in this massive 
seedling, the pith appearing in the midst of the xylem at about 1 cm. 
below the collet. The pith rapidly enlarges, and dilates the xylem into the 
form of a ring which soon opens on one side, the corresponding phloem 
dividing into two at the same time. Thus at 3 mm. below the collet there 
is a C-shaped band of xylem with four protoxylems, and five phloem 
groups (Fig. 4). The xylem-band then begins to break up into detached 
pieces in the way indicated by the dotted lines in Figs. 4 and 5 : the result 
being the production of two triads, each consisting of a median protoxylem 
and a pair of lateral metaxylems, and each destined to become the middle 
vein of one cotyledon ; and also of two curious bundles, each consisting of a 
single metaxylem group with a laterally attached protoxylem, these later 
dividing and becoming the lateral veins of the two cotyledons. There are 
now six phloems, one superposed upon each metaxylem (Fig. 6). It is seen 
that the opening of the xylem-ring on one side only and the formation of a 
C-shaped band is merely a precocity ; and at the level of the collet the 
vascular system has again become practically symmetrical : this irregularity 
is, however, of fairly constant occurrence. 
1 de Vries (’ 95 ), where a number of seedlings are figured; and (’ll), p. 466. 
2 Chauveaud ( 11 ), p. 414. 3 Reinke (’ 71 ), p. 11. 
