Vascular 'System of Matonia pectinata . 517 
cyclic Ferns in which internal strands arise in the same manner. These 
accessory vascular strands are to be regarded as essentially new develop- 
ments, which partially replace the pith, just as the pith at an earlier stage 
replaced the internal vascular tissues. They are parts of the stele, just 
as the pith is part of the stele, which has now become a complicated 
structure without losing its individuality 1 . 
1 It is abundantly clear that the term stele must be restricted to the central cylinder of the axis, 
if it is to retain a morphological meaning, and that the concept of polystely, at least in the Ferns 
proper, must be definitely regarded as obsolete. We have expressly excluded the other cases of so- 
called polystely, Selaginella , Primula , Gunner a, Nymphaeaceae, &c., a discussion of which would 
be out of place here. The idea put forward by Van Tieghem and Douliot, that several equivalent 
cylinders in a stem could arise by the successive forking of the original one found at its base, was 
upset by the work of Leclerc du Sablon and Jeffrey, who showed that the real origin of the so-called 
‘ polystelic ’ condition was quite different. It is doubtful, indeed, if the concept of homology could 
in any case be applied to the different vascular strands called steles By Van Tieghem and Douliot, 
whatever their origin. From the nature of the case they certainly could not be morphologically 
equivalent in the evolutionary sense, which is the only accurately definable and consistent meaning 
we can attach to the word homology. But since the state of things on which the theory of polystely 
was based is, so far as we know, non-existent, there is no need to discuss it further. For the reasons 
given we have avoided applying the term stele to the internal cylinders of Matonia, considering 
them as accessory developments of the original ancestral stele, and as parts of the present com- 
plicated stele. 
