332 Shaw . — The Seedling Structure of Araucaria Bidwillii. 
There yet remains to be considered the seedling which showed the 
anomalous structure. Two points stand out clearly in this— the occurrence 
of inverted vascular tissue, and the production of several steles. In another 
group of plants, the Cycads, Worsdell (6) considers that the presence 
of inverted vascular bundles is evidence of the derivation of these plants 
from polystelic ancestors, the inverted vascular bundles in modern Cycads 
being interpreted as the remnant of the interior portion of a formerly con- 
centric stele whose peripheral segment forms part of the normal vascular 
ring. It is interesting to note that the polystelic stage in Araucaria 
Bidwillii is derived from a stage with inverted vascular tissue, this inverted 
vascular tissue forming the segment of each stele lying nearest the centre of 
the root. Thus the inverted vascular tissue gives rise to that part of each 
stele which it should do if Worsdell’s theory of the Medullosean origin 
of Cycads is correct. 
The value to be attached to this abnormal anatomy depends upon the 
value which we attach to seedling anatomy as a phylogenetic criterion, and 
not less on the still wider consideration as to the phylogenetic value of 
teratological phenomena in general. 
As a rule it has been shown that deviations from the normal number 
of protoxylems and of cotyledonary bundles should not be made the basis 
of phylogenetic speculation ; they are probably correlated with other, and 
more local, factors in the development of the seedling. The question 
remains how far the habit of the seedling can influence the development of 
its vascular tissue ; that variable conditions can under normal circumstances 
influence the amount produced seems clear, but whether the more striking 
abnormalities in structure are due to the same cause is doubtful. 
Worsdell postulates that of all the regions in a plant likely to show 
ancestral traits the cotyledonary or first node is one of the most favourable. 
He cites the case of Encephalartos Bar ter i , which showed three steles 
in the hypocotyl, a structure which he considers as recalling Medullosean 
ancestry. Are we to attach the same meaning to the polystely of Araucaria 
Bidwillii ? The part played by the inverted vascular tissue in the formation 
of the stele certainly favours this view. On the other hand, is there any 
external feature in the seedling which distinguishes it from the normal type 
and would point to its having grown under different conditions ? A refer- 
ence to Diagram VI, Fig. 9, shows at once the peculiarity of the specimen 
which has already been described (p. 327). The polystelic zone (i.) occurs 
in the upper part of the root, which is here horizontal, the base of the 
hypocotyl having been sharply bent, and immediately precedes a sharp con- 
striction beyond which the root is much thinner and of the normal diarch 
type. Whether this constriction necessitates diarch structure in the subse- 
quent and thinner part of the root, and therefore the rapid production 
of this from a closely adjoining part with hexarch structure leads to the 
