445 
Seedling Structure of Gymnosperms. III. 
root-structure (Diagram 3, Fig. 7). A precisely similar vascular rearrange- 
ment takes place in the region of b leading to the formation of the third 
pole of the tri&rch root-structure (Diagram 3, Fig. 8). In no case has 
a definite rotation of the protoxylem been made out ; this tissue occupies 
its final position chiefly by the dying out of the metaxylem elements which 
would otherwise be in the way. 
From the above facts it is seen that the vascular tissue from the smaller 
cotyledon forms one pole of the triarch root, while the other two poles are 
formed from the bundles of the larger seed-leaf. In this process the relative 
contributions of the different strands varied ; and although in the later 
stages of the transition, owing to the compactness of the cylinder, it is 
almost, and sometimes quite, impossible to accurately delimit one strand 
from another, the positions of the xylem poles of the root, when compared 
with the relative positions of the seed-leaf traces, point to the fact that, in 
the seedling described, the bundles £, c , and e are more important than 
a and d. 
As in Macrozamia an endodermis does not appear until a much lower 
level has been reached. 
Worsdell found that the upper part of the primary root was triarch 
which appeared to be reduced to a diarch structure towards the apex ; this 
was not so in the example described above, the dissimilarity is probably due 
to the difference in age between the seedlings investigated. Matte found 
that in one example the root was diarch at its base which, by the organiza- 
tion of another pole, became triarch nearer the apex ; while in an older 
seedling he found that ‘ la structure-racine, avec apparition de deux poles 
tracheens, s’etablit un peu plus bas, en meme temps que, toujours sous 
l’influence des recloisonnements tuberisants, les lames radiales libero- 
ligneuses secondaires s’espacent notablement les unes des autres avec con- 
tournements frequents de leurs elements constituants. 
{ Vers le bas cet espacement s’accentue regulierement et aboutit finale- 
ment, a des niveaux tres espaces, a la formation de trois, puis de quatre 
masses a peu pres egales, avec differentiation progressive d’un troisieme, puis 
dun quatrieme pointement tracheen suivant le mode indique precedemment. 
‘ A un centimetre de la pointe, la structure primaire subsiste seule et, 
contrairement a ce qui se passe dans la germination a [the younger seed- 
ling referred to above], les quatre poles sont reunis entre eux par un bois 
primaire compact occupant tout l’axe de la racine.’ 1 
In a footnote he makes the following observation : ‘ On remarquera que 
le nombre des poles radicaux, de plus en plus grand a mesure qu’on se 
dirige vers 1 ’extremite de la racine chez le St. paradoxa , devient au contraire 
de plus en plus petit, dans ce meme sens, chez Ceratozamia mexicana 
These are significant statements, more especially in view of the like 
1 loc. cit. p. 44. 
