i 70 Blackburn On the Vascular Anatomy of 
elements are differentiated. There is marked tangential extension of the 
phloem elements at a very early age. 
R. gramineus. The cambium does not appear quite so early in this 
species, and thus some of the primary elements may be distinguished (see 
Text-fig. 14). Both internal and external endodermis can be demonstrated in 
the older seedlings (see Text-fig. 16). The tangential extension does not take 
place to any great extent as there is little increase in girth of the stem (cf. 
Text-figs. 13 and 1 5 with 14 and 16 on the same scale). The axis in this and 
other species is very telescoped, and in consequence the wood elements are 
short and the strands sinuous in their course. There are no distinct 
principal rays between the bundles, so that their identity is almost lost. 
Text-figs. 15 and 16. Ranunculus gramineus. First plamular internode at two stages. 
The same seedlings and magnification as in Text-figs. 13 and 14. 
R. bulbosus shows separate strands at an early stage, and in general 
resembles R. gramineus . 
R. auricomus is similar to R. gramineus . The individuality of the 
primary strands is more obvious in this species. 
R. repens shows extreme tangential stretching of the vascular elements, 
even in the very young stages, so that the long dimensions of the tracheides 
appear in transverse section. This seems to be due to the fact that the 
vascular cylinder is wider than it is long. 
3. The aquatic species possess elongated internodes (except the first) 
in which there are distinct and separate vascular bundles. 
R. sceleratus . There are six definite strands in the internode. There 
is a tendency for these to be lost at the node, but at the cotyledonary node 
