618 TRANSACTIONS OF THE CANADIAN INSTITUTE, [VoL. VI. 
and only in rather stout young hypogzous stems does it become quite 
obsolete. 
Photograph 15, plate 9, represents a section through the upper region 
of the stem of a well-advanced seedling. Phloroglucin and hydro- 
chloric acid have been used to bring out the lignified phlceoterma 
which can be clearly distinguished on the outer margin of the fibro- 
vascular segments, but less distinctly along their inner border. The 
occurrence of an internal phlceoterma in the young fibro-vascular cylinder 
of a species in which it is absent in the mature hypogzous stem, is of 
considerable morphological interest. In the aerial shoots, the phlceo- 
termal boundaries are no longer distinguishable histologically, although 
on morphological grounds they should doubtless be regarded as never- 
theless present. 
Even in the quite young stem of R. rhombordeus, there is no trace of 
an internal phlceoterma. However, by examining the youngest region 
of the axis, a quite distinct internal phlceoterma may be demonstrated. 
Photograph 17, plate 9, represents a cross section of the young stem 
where the fibro-vascular cylinder appears as an unbroken ring. Photo- 
graph 18, plate 9, shows a tranverse section of the stelar tube where it is 
interrupted by a foliar gap; the junction of the internal and external 
phlceotermal layer around the sides of the foliar gap can be clearly 
discerned. Photograph 16, plate 9, represents a section through an 
older region of the subterranean stem; three foliar gaps are to be seen 
and the internal phlceoterma has now become quite obsolete. The 
aerial shoots of this species do not differ materially in the structure of 
their vascular strands from the other species already described. &. 
rhombordeus is distinguished from all the species examined by the com- 
plete disappearance of any histological evidence of the existence of an 
internal phlceoterma, even in quite young stems. Even here, the 
boundary of the cortical tissues on the inside of the stelar tube may 
readily be determined by examining the stem in a very early stage of 
development. 
The writer has not been able to secure seedlings of other species of 
Ranunculus, but those described appear to be sufficiently varied in their 
affinities to afford reliable data for conclusions as to the correct morpho- 
logical interpretation of the central cylinder of this genus. These 
deductions may, however, be advantageously deterred until the allied 
genus Anemone, has been considered. 
As has been already mentioned, Van Tieghem states that certain 
species of Anemone have a medullated monostelic central cylinder, 
