736 Gw y nne- Vaughan, — Observations on the 
plant (1. c. p. 312) ‘is very closely related to Euhypolepisl it 
may confidently be removed to that genus. 
Upon the whole, therefore, Prantl receives considerable 
support from our results, since nearly all of the genera re- 
garded by him as relatively primitive in their respective family 
branches also prove to be characterized by the possession of 
a primitive vascular structure, especially as regards his first 
two tribes. Nevertheless, this must not be taken to mean 
that each, or even any, of his tribes actually represent separate 
single lines of descent. Much further research is necessary 
on all sides before this question can be satisfactorily faced, 
and the above discussion merely serves to point out the fact 
that anatomical considerations must play an important part 
in coming to any conclusion. 
Conclusion. 
The stelar theory has undergone many modifications under 
the hands of different authors since it was first introduced by 
Van Tieghem, and the exact meaning of the word ‘ stele * as 
now used is getting somewhat obscure. It is, however, 
becoming more and more apparent that the chief value of the 
conception lies in its ontogenetic and phylogenetic significance, 
whereby the stele of the stem may be regarded as the central 
cylinder of the young plant and all those tissues of the mature 
axis that result from its modification, or, as Farmer and Hill 1 
would prefer to have it, the central cylinder of the young 
plant and all those vascular tissues of the mature axis that 
result from its modification. As a consequence of the first 
point of view it must also be held that there exists a regional 
distinction of primary importance between the stelar tissue 
and the cortex. Therefore, when considering a vascular 
arrangement such as a dictyostele or a solenostele it becomes 
impossible to neglect the question, whether the central paren- 
chyma is to be regarded as stelar, and therefore morphologi- 
1 On the arrangement and structure of the vascular strands in Angiopteris 
evecta and some other Marattiaceae, Annals of Botany, vol. xvi, no. 62, p. 
392, 1892. 
