Seedling Struchire of Gymno sperms. III. 447 
of each of the petioles of the cotyledons may be said to join two by two. 
Just before reaching the central cylinder the inner strands of each fuse, and 
the outer strands of the one fuse with the outer strands of the other, the 
four strands thus formed giving rise to the four protoxylem groups \ 
Series A. The top of the hypocotyledonary axis is occupied by nine 
cotyledonary traces, five derived from one seed-leaf and four from the other 
(Diagram 4, Fig. 3, a . . . i). These pass with some degree of rapidity 
towards the centre, and the three traces b } c, and d, derived from the larger 
cotyledon, fuse to form one structure ; at the same level e and f, of the 
smaller seed-leaf, have approached one another pretty closely (Diagram 4, 
Fig. 5). At a lower level e and / effect a junction as they enter to form 
part of the central cylinder, and so also do the bundles^ and h (Diagram 4, 
Fig. 6). The strand a enters the cylinder by itself and so also, at a lower 
level, does i. The vascular cylinder is now concentric, and the bundles 
have lost their identity, that is to say it is impossible to delimit their 
boundaries with absolute certainty. 
The organization of the root-structure proceeds rapidly, two xylem 
poles, in the plane of the cotyledons, are differentiated quickly ; then two 
other poles in the intercotyledonary plane are formed. The phloem is 
still intact ; but, as soon as these last xylem rays are produced, the bast 
divides first opposite the xylem rays first differentiated, and then, at a lower 
level, opposite the intercotyledonary poles. 
With regard to the relative value of the cotyledonary strands in the 
formation of the root-structure, g and h together form one pole ; e and f 
another pole ; z, by itself, the third ; and b and c, the fourth pole. The 
strands c and d appear to be of no particular value. A comparison of 
Diagrams 2 and 4 shows that the transition of this example of Dioon edule 
and Macrozamia is in many respects identical. 
Series B. This seedling differed from the first in the fact that the 
hypocotyl, at its upper end, had eight vascular strands, an equal number 
being derived from each seed-leaf. The behaviour of each of these was very 
regular : the bundles of each cotyledon consist of a central pair which is 
bounded on either side by one strand. Each central pair of traces organize 
that pole of the root-structure situated in the plane of the cotyledons ; and 
each of the lateral bundles gives origin to one pole so that a hexarch root- 
structure results. There is thus a considerable difference between these two 
seedlings of Dioon edule. On the other hand there are important points of 
similarity between them. In each case those two poles of the root-structure 
situated in the plane of the seed-leaves was organized first and were the 
strongest ; those poles in the intercotyledonary plane were differentiated at 
a lower level ; further, the division of the phloem-ring first took place 
opposite the two protoxylem rays first organized. 
In no case has a rotation of the protoxylem been seen, the remarks on 
