675 
certain Orders of the Ranales. 
pass across and fuse with those on the dorsal side, the leaf-base almost 
completely encloses the stem, and its median bundle, which is three or four 
times the size of the others, is the first to join in the stem-cylinder 
(Figs. 49-52). 
Hydrastis canadensis , L. 
This plant appears to me more allied to Berberidaceae than to Ranun- 
culaceae, hence I prefer to include it here. The morphological and 
anatomical structure is exceedingly like that of Podophyllum. In the 
flowering stem is the same scattered monocotyledonous vascular system 
consisting of three ranks of bundles, which tend to become confused 
here and there ; some of the bundles of the middle rank are larger than 
those of the inner rank. The same structure occurs in both peduncle and 
petiole (Fig. 48). 
Bibliography. 
Bastin : Structure of Podophyllum, Amer. Journ. Pharmacy, 1896. 
Col : Recherches sur la Disposition des faisceaux dans la tige et les feuilles de quelques 
Dicotyledones. Ann Sci. Nat, ser. 8, vol. xx, 1904, p. 116. 
Holm, Th. : Podophyllum peltatnm : a morphological study. Bot. Gazette, vol. xxvii, 1899, p. 419. 
Plitt : loc. cit. 
Vesque : loc. cit. 
Discussion on the Vascular Structure of the above Orders. 
A comparative study of the essential and general features of the 
vascular structure of these orders has, for my own mind, at any rate, thrown 
no small amount of light, not only on the vascular structure of the group as 
a whole, but also on certain peculiar and characteristic features of some of 
the orders of which no explanation has hitherto been forthcoming. And 
yet these characters are surely of sufficient interest and peculiarity to war- 
rant the awakening of some curiosity as to their meaning and origin. It is 
high time we ceased to be content with the mere observation and recording 
of structures, and endeavoured to probe into their essential nature and 
relationships. The first point which accrues as a result of my study of 
these orders is that the primitive and original vascular system of the leaf 
and, consequently, that of the stem as (on the phyton theory which 
I uphold) a product of that of the leaf, is the complete cylinder of collateral 
bundles enclosing a medullary system of strands primitively amphivasal in 
structure. This structure we find preserved in its pristine purity 1 in 
certain Ranunculaceae and Berberidaceae, plants which are also primitive as 
regards the structure of their floral organs. In the Ranunculaceae we can 
trace the steps by which this original structure has become modified, both 
in the stem and leaf. The scattered or medullary system disappears first 
1 But the amphivasal bundle-structure has for the most part been lost. 
Z Z 2 
