1898-99.] |. MORPHOLOGY OF THE CENTRAL CYLINDER IN THE ANGIOSPERMS. 629 
co-exist in different species of the same genus. For example, Ranunculus 
aquaitls is, according to his view, astelic, and XR. abortivus is, on the 
other hand, medullated monostelic. Strasburger has questioned the 
possibility that the pith in different species of Ranunculus should be 
sometimes extrastelar (in the astelic type), and intrastelar (in the 
monostelic type). He prefers to consider that the medulla is always 
intrastelar, and that, consequently, the individual endodermal sheaths 
in the species of Ranunculus, where they occur, are different morpho- 
logically from the’ phlceoterma, which he supposes surrounds the 
complex of bundles in the so-called medullated monostelic types. 
The writer’s examination of the development of a number of species 
of Ranunculus and Anemone has shown that in the young axis the 
stelar system possesses an internal phlceoterma which is continuous 
with the external phlceoterma through the foliar gaps, and is therefore 
of the same morphological value. In some species the internal phlceo- 
terma disappears in the older region of the stem, eg., RX. abortivus and 
R. rhomboideus, and the stelar axis then appears to be monostelic. A 
study of its development, however, shows that it is primitively astelic. 
This view of the matter quite removes the difficulty of having to 
regard the pith in some species of Ranunculus and Anemone as intra- 
stelar and in other species as extrastelar, because their ontogeny 
shows that the pith is in both cases extrastelar, z¢., ordinary 
fundamental tissue which has been enclosed by the stelar tube. In the 
older stem of various species of Ranunculus and Anemone, both 
external and internal phlceotermas disappear when there is much 
sclerenchymatous tissue present in the vascular system. It is probably 
not going too far to state as a result of the study of development that 
in the genus Ranunculus the pith is throughout extrastelar. In 
consequence of his detailed anatomical study of the order Ranunculacee, 
Marié" has come to the conclusion that the genus Ranunculus is the 
stock from which all the other genera of Ranunculacee have taken 
their origin. It will probably not be an easy matter to demonstrate 
the existence of an internal phlceoterma even in the young stems of 
the various ranunculaceous genera, especially where there is much 
sclerification of the central cylinder or much secondary growth, since 
even the external phlceoterma under these circumstances is nearly 
always with difficulty distinguishable. It is not unlikely, however, that 
the internal phlceoterma will be found to persist in the more conserva- 
tive vascular system of the floral axes. In any case, there appear to be 
51. Op. Cit., p. ro8. 
