402 Chandler . — On the Arrangement of the Vascular Strands 
parenchyma is wholly distinct from the external or cortical parenchyma. 
In the light, however, of G wynne- Vaughan’s and Jeffrey’s work, this view 
is, to many, somewhat difficult of acceptance. The weak point in the con- 
ception is the implied distinction drawn between the parenchyma outside 
and the parenchyma inside the ring of vascular strands. There seems to be 
no reason why any such distinction should be drawn between tissues which 
are shown by a study of the young plant to be part and parcel of one and 
the same thing, viz., the general ground-tissue. 
The next view is that of Farmer and Hill 1 as put forward in their 
paper on Angiopteris evecta . Acknowledging the importance of Jeffrey’s 
work in bringing the vascular system as a whole to the fore in all ‘ stelar ’ 
questions, the authors point out that the weakness of Jeffrey’s theory is the 
retention of the endodermis as an indispensable constituent of the primitive 
siphonostele. As a result of their work on the Marattiaceae, and from the 
evidence afforded by Helminthostachys , Botrychium , and Osmunda as to the 
unreliability of the endodermis as a morphological criterion, the authors 
maintain that in dealing with all so-called stelar questions, tissues of two 
categories only need to be considered, viz., vascular and non-vascular. 
Schoute, in his memoir already quoted, deals with the question in 
a very exhaustive manner. Not the least important service rendered by 
the author in this valuable essay, is his emphasizing a fact which is very apt 
to be overlooked, viz., that the results of modern research after all only 
confirm the main contention of Van Tieghem that the monostele is the 
primary structure in all vascular plants. This author, however, criticizes 
Van Tieghem’s stelar theory from two points of view; firstly, from a study 
of the development of the plant, both from the embryo and from the grow- 
ing point of the adult, and, secondly, from the point of view of comparative 
anatomy. As a final result of his work, Schoute concludes that ‘ in Stengel 
und Wurzel der Gefasspflanzen findet sich ein einziger Stelar-Typus, die 
Monostelie.’ 
Having thus briefly outlined the present position of the stelar question, 
the writer may perhaps be allowed to consider the bearing, if any, which 
the results of his investigations have upon the question. 
The simplest type of vascular elaboration above described is (with the 
exception of Polypodium aureum) that of such a fern as Doodia aspera. It 
will be remembered that the primary condition of the vascular system 
is a solid vascular rod, which later appears with a central strand of tissue 
which is undoubtedly phloem. The differentiation of this central phloem 
in no way alters the essential character of the young cauline strand, which 
is that of a solid rod of vascular, as opposed to non-vascular, tissue. Follow- 
ing upon the appearance of the central phloem we have the formation 
of several leaf-traces which leave no real gaps in the ordinary sense of the 
1 Loc. cit. 
