446 
Hill and de Fraine. — On the 
observations and theoretical conclusions of Shaw 1 on Araucaria Bidwillii , 
and the similar facts recorded by others besides ourselves both for Gymno- 
sperms and Angiosperms. It is, however, not desired to discuss them here ; 
their theoretical importance will be considered in our general conclusions. 
Dioon. 
Dioon edule , Lindl. 
The seedling has been described and figured by Matte 2 and Thiessen, 3 
with whose observations we are in agreement. It resembles the seedlings 
of other Cycads, e. g. Macrozamia , very closely both as regards its general 
appearance, and also in its internal structure, with the minor exception that 
in Dioon the mucilage canals and secretory cells are more numerous. 
The seed-leaves are closely apposed one to the other, but the line of 
demarcation is always obvious. At their apices the cotyledons are very 
irregular in outline, and there is no definite arrangement in the disposition 
of the vascular bundles (Diagram 4, Fig. i) ; at a lower level the strands 
take up a normal position, when it is seen that the larger seed-leaf has more 
bundles than the smaller. Following the traces downwards they are seen 
to become reduced in number which is brought about by the fusion of the 
extreme laterals. Thus, in one case, at the apex of the seed-leaves there 
were seven and six bundles respectively, but, at the base, the numbers were 
five and four (Diagram 4, Fig. 3) ; in another instance each cotyledon had 
four strands at the cotyledonary node. 
These observations are of the same nature as those of the two authors 
cited above. Thus Thiessen remarks that the tip of each cotyledon has 
one concentric strand which abuts immediately against the epidermis. At 
lower levels this bundle divides into eight, which fuse in pairs so that four 
strands result. In two seedlings it was found that one of the cotyledons had 
five bundles at its base. 
In the two seedlings described by Matte, one had four traces in each 
cotyledon, while the other example had four in one seed-leaf and two in the 
other together with two much smaller ones which, in the hypocotyl, fused 
on to the nearest plumular traces and played no part in the transition ; the 
resulting root-structure was triarch, while in the former case it was tetrarch. 
Both authors enter fully into histological details, which it is not 
proposed to consider here. 
Transition. 
Matte and Thiessen also describe and illustrate, more or less briefly, 
the transition-phenomena. The latter writer remarks that ‘the four strands 
1 Shaw : The Seedling Structure of Araucaria Bidwillii (Ann. Bot., xxiii, 1909). 
2 Matte: Recherches surl’appareil libero-ligneux des Cycadacees (Caen, 1904). 
3 Thiessen : The Vascular Anatomy of the Seedling of Dioon edule (Bot. Gaz., xlvi, 1908). 
