654 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VoL. VI. 
individual endodermal sheaths. By this process the pith is supposed 
to become continuous with the extrastelar fundamental tissue, and the 
central cylinder disappears as such. 
Van Tieghem states that of closely allied species some may have a 
medullated monostelic central cylinder, while others have the astelic 
type of central cylinder. For example, in the Equisetacee, 2. arvense 
is monostelic, Z. ¢zmosum,on the other hand, is astelic. Among the 
Phanerogams, Ranunculus aquatilis and R. Lingua are described as 
having an astelic central cylinder, while a number of other species, ¢.g., 
R. acris and RX. abortzvus,are monostelic. In the genus Anemone, parallel 
cases are presented by A. xemorosa, which is astelic, and A. pennsyl- 
vanica which is monostelic. It has been pointed out in the introduction 
that Van Tieghem in more recent publications has abandoned the idea 
that any of the Ophioglossaceze or Equisetaceze are medullated mono- 
stelic, but, on the contrary, regards them as astelic throughout the 
epicotyledonary region of the stem. Although he has given up the 
view that the cauline central cylinder of these Cryptogams is in any 
case medullated monostelic, he is still of the opinion that certain 
ranunculaceous genera” present examples of both the above-men- 
tioned types of central cylinder. 
Before going on to submit Van Tieghem’s views in regard to the 
morphology of vascular strands of certain Ranunculacez to the test of 
their agreement with the facts of anatomy and development, it is 
necessary to describe certain modifications of these views which have 
recently been proposed by Strasburger* and which have already been 
accepted by many botanists of eminence. Strasburger admits the great 
morphological value of Van Tieghem’s definition of the central cylinder. 
He suggests, however, inasmuch as the innermost layer of the cortex 
which bounds the central cylinder is not always an endodermis, 
7.é., a layer of cells provided with. a cutinized undulating radial 
band, but is very often composed of sclerenchymatous elements or 
starch-bearing cells, that some general name is desirable for the internal 
layer of the fundamental tissue adjoining the central cylinder. He 
suggests the term phlceoterma as a suitable designation of the innermost 
layer of the cortex, no matter what its histological character may be. 
Strasburger questions the possibility of different species of the same 
genus having in some cases a medullated monostelic central cylinder, 
and in others presenting the astelic type of arrangement of their vascular 
tissues. In other words, he believes it impossible that the medullary 
33. Eléments de bot., 1898, p. 179. 
34. Histolog. Beitrage III, pp. 309-313, 442, 443, 484-486. 
Vs 
1 ageroeeal 
